Orthopedics

Feature Article Supplemental Data

Complications, Additional Surgery, and Joint Survival Analysis After Medial Open-Wedge High Tibial Osteotomy

Furkan Yapici, MD; Umit Selcuk Aykut, MD; Mehmet Coskun, MD; Muhammet Coskun Arslan, MD; Demet Merder-Coskun, MD; Ahmet Kocabiyik, MD; Erman Ulu, MD; Avni Ilhan Bayhan, MD; Mehmet Akif Kaygusuz, MD

Abstract

The reported incidence of complications following medial open-wedge high tibial osteotomy (MOWHTO) varies. The authors sought to assess the complications, additional surgeries, and joint survival following MOWHTO in patients with isolated medial compartment arthrosis during a mean follow-up of 10 years. This retrospective study involved patients implanted with spacer plates, angle adjustable plates, or inverse L-type plates with wedges between 2000 and 2010. A total of 504 knees from 441 patients were examined. Mean age of the study population was 52.6±7.0 years, with 56 (11.1%) knees from men and 448 (88.9%) from women. The 10-year Kaplan–Meier joint survival rate was 94.8%. Overall complication rate for MOWHTO was 63.7%, with complications in 20.3% of treated knees requiring additional surgery. In this population, although the overall complication rate and the need for additional surgery were high, the need for additional surgery resulting from serious complications was low (2.6%). The high joint survival rate and low rate of additional surgery for serious complications indicate that MOWHTO can be safely applied in patients with isolated medial gonarthrosis. [Orthopedics. 2020;43(5):303–314.]

Abstract

The reported incidence of complications following medial open-wedge high tibial osteotomy (MOWHTO) varies. The authors sought to assess the complications, additional surgeries, and joint survival following MOWHTO in patients with isolated medial compartment arthrosis during a mean follow-up of 10 years. This retrospective study involved patients implanted with spacer plates, angle adjustable plates, or inverse L-type plates with wedges between 2000 and 2010. A total of 504 knees from 441 patients were examined. Mean age of the study population was 52.6±7.0 years, with 56 (11.1%) knees from men and 448 (88.9%) from women. The 10-year Kaplan–Meier joint survival rate was 94.8%. Overall complication rate for MOWHTO was 63.7%, with complications in 20.3% of treated knees requiring additional surgery. In this population, although the overall complication rate and the need for additional surgery were high, the need for additional surgery resulting from serious complications was low (2.6%). The high joint survival rate and low rate of additional surgery for serious complications indicate that MOWHTO can be safely applied in patients with isolated medial gonarthrosis. [Orthopedics. 2020;43(5):303–314.]

Osteoarthritis will be the fourth leading cause of disability in 2020.1 It is estimated that knee osteoarthritis affects 10% of the population older than 55 years, from which 1 in every 4 patients is severely disabled, which results in a high social and economic cost.2 Radiographic studies of US and European populations 45 years and older show higher rates for osteoarthritis of the knee (14.1% for men and 22.8% for women) compared with younger populations.3 Gonarthrosis is a natural result of malalignment.4 The goal of the high tibial osteotomy (HTO) of a malaligned knee is to transfer the load distribution from the medial compartment with arthrosis to the intact lateral compartment.5 Moreover, HTO can be applied in the absence of varus gonarthrosis to replace the tibial slope in patients with anterior, posterior, posterolateral, or complex instability and to provide decompression in the medial compartment in patients with spontaneous osteonecrosis, osteochondritis dissecans, or medial meniscus transplantation.6

Although HTO was initially developed as a closed-wedge technique, medial open-wedge HTO (MOWHTO) has become more widely used due to its use of locked plates and its relatively simple application. Complications that have been reported following MOWHTO include lateral cortex fracture (LCF), lateral plateau fracture (LPF), plate (implant) irritation, loss of correction, undercorrection, overcorrection, delayed union, nonunion, pseudoarthrosis, superficial and deep infection, neurovascular injury, deep venous thrombosis, intra-articular screw, implant failure, delayed wound healing, tibial slope change, joint stiffness, complex regional pain syndrome types 1 and 2, compartment syndrome, cardiopulmonary complications, urinary infections, peroneal paresis, bone graft donor site pain, patella infera, tibial plateau necrosis, iliac crest fracture, saphenous nerve neuroma, and flexion contracture.7–13 The reported incidence of these complications varies, so the incidence of complications associated with MOWHTO remains unclear; therefore, it is not known whether this technique can be safe.

Understanding the potential complications of this technique may be essential to obtaining better clinical outcomes. The aim of this study was to determine the complications and joint survival rate associated with MOWHTO in patients with isolated medial compartment arthrosis during a mean follow-up of 10 years. The novel aspect of this study was the combination of different aspects of complications that were studied separately before. Types of union (normal, delayed, nonunion), the mean union time, mean correction angle, graft use, correction type (undercorrection, planned correction, overcorrection), and other general complications were not established together by previous works.

Materials and Methods

Approval was received from the Ethics Committee of Metin Sabanci Baltalimani Bone Diseases Education and Research Hospital, Istanbul, Turkey, for retrospective evaluation of MOWHTOs that were performed between 2000 and 2010 with the use of Anthony plates (Anthony-K, Clamart, France),14 Puddu plates (TST; Pendik, Istanbul, Turkey), and Esenkaya L-type plates (Hipokrat; Pinarbasi, Izmir, Turkey).15

Surgical indications for MOWHTO at the authors' institution were as follows: symptomatic proximal tibial (primary) varus deformity and isolated medial gonarthrosis; range of motion of 120° or greater; flexion contracture less than 5°; body mass index less than 35 kg/m2; Kellgren–Lawrence grade 1, 2, or 3 if the lateral compartment of a knee was proven healthy and suitable for MOWHTO with arthroscopy; had an arthroscopy study available for evaluation; had double varus (primary varus deformity plus central ligament insufficiency [anterior cruciate ligament/posterior cruciate ligament]) or triple varus (primary varus deformity plus central ligament insufficiency plus posterolateral corner insufficiency); and had primary varus deformity with an osteochondral lesion (treated with curettage and microfracture or mosaicplasty). There was no age limit. The authors believed that physiologic age, which depends on body habitus, culture, lifestyle, eating and sports habits, and self-preservation, is more important than chronologic age.

Exclusion criteria for the study were anterior cruciate ligament or posterior cruciate ligament injury, implantation of conventional plates or allograft and synthetic grafts, bilateral surgery in the same session, ligament reconstruction or mosaicplasty combined with MOWHTO, follow-up less than 84 months, and death. Patients with anterior cruciate ligament, posterior cruciate ligament, or any other ligament reconstruction and mosaicplasty combined with MOWHTO were excluded to determine the pure results of MOWHTO operation for isolated medial compartment arthrosis. Patients with bilateral surgery in the same session were excluded due to the difference in rehabilitation protocol between unilateral and bilateral surgery, which may affect the results. The time period between bilateral staged surgery was at least 1 year. Patients who underwent the bilateral staged surgery were fully recovered from the initial MOWHTO before undergoing the second. Patients with implantation of conventional plates or allograft and synthetic grafts were excluded due to the relatively small number of patients. Patients treated with MOWHTO and a conventional plate were excluded because the design did not meet the expectation of modern orthopedic osteotomy fixation, which would have an adverse effect on the results. Patients with less than 7 years (84 months) of follow-up were excluded to determine the long-term results. Deceased patients were excluded to determine joint survival.

Complications occurring during follow-up were classified into 3 grades according to severity, similar to the classes described by Martin et al.8 Specifically, in accordance with that classification, grade 1 minor complications (LCF, undercorrection, overcorrection, broken screw with conservative follow-up, and iliac crest fracture) were those that did not require additional treatment. Complications that required short-term nonsurgical treatment (delayed union, superficial infection, nondisplaced LPF or nonunion with conservative follow-up, deep venous thrombosis, and tibial tubercle fracture) were classified as grade 2 moderate. Grade 3 major complications (implant irritation, deep infection, lateral crural hypoesthesia, displaced LPF, tibial nerve neuropraxia, iatrogenic popliteal artery injury, intra-articular screw, and broken screw with implant failure) required long-term treatment or surgical treatment or represented a permanent injury. Survival was assessed by whether there was a requirement for arthroplasty.

In addition, 2 subgroups were added to grade 3 major complications: grade 3 major complications requiring additional surgery and serious complications requiring additional surgery. Lateral crural hypoesthesia and tibial nerve neuropraxia were excluded from grade 3 major complications requiring additional surgery due to the requirement of a long-term treatment but not an additional surgery. Due to the need for re-surgery (as all patients with implant irritation have undergone implant removal), implant removal due to plate irritation was included in grade 3 major complications and grade 3 major complications requiring additional surgery. However, it was excluded from serious complications requiring additional surgery because it is not a serious complication (ie, implant removal due to irritation is a major but not serious problem).

The lateral tibiofemoral angle (LTFA) was defined as the lateral angle between the anatomical axes of the tibia and femur (Figures 12). The desired correction of the LTFA was to between 174° and 165°. According to the postoperative evaluation, overcorrection was considered to correspond to an LTFA less than 165° and under-correction was considered to correspond to an LTFA greater than 174°.

Determination of the proximal and distal midpoints of the femur and tibia for anatomic axes. Preoperative anteroposterior orthoroentgenograph of the pelvis showing how the midpoint of cortices below the lesser trochanter was used for the proximal femur (A). Preoperative anteroposterior orthoroentgenograph of the knee showing how the apex of the femoral notch was used for the distal femur and how the center of the tibial spine was used for the proximal tibia (B). Preoperative anteroposterior orthoroentgenograph of the ankle showing how the center of the talus was used for the distal tibia (C).

Figure 1:

Determination of the proximal and distal midpoints of the femur and tibia for anatomic axes. Preoperative anteroposterior orthoroentgenograph of the pelvis showing how the midpoint of cortices below the lesser trochanter was used for the proximal femur (A). Preoperative anteroposterior orthoroentgenograph of the knee showing how the apex of the femoral notch was used for the distal femur and how the center of the tibial spine was used for the proximal tibia (B). Preoperative anteroposterior orthoroentgenograph of the ankle showing how the center of the talus was used for the distal tibia (C).

Preoperative anteroposterior orthoroentgenograph measurement of the lateral tibiofemoral angle, defined as the lateral angle between the anatomic axes of the tibia and femur. The lines on the leg on the right represent anatomic axes of the femur and tibia.

Figure 2:

Preoperative anteroposterior orthoroentgenograph measurement of the lateral tibiofemoral angle, defined as the lateral angle between the anatomic axes of the tibia and femur. The lines on the leg on the right represent anatomic axes of the femur and tibia.

For radiologic evaluation, preoperative comparative anteroposterior and lateral weight-bearing knee radiographs and orthoroentgenographs, first-day postoperative anteroposterior and lateral non–weight-bearing knee radiographs, week 6 comparative anteroposterior and lateral weight-bearing knee radiographs, and last follow-up comparative anteroposterior and lateral weight-bearing knee radiographs and orthoroentgenographs were used. Anteroposterior and lateral knee radiographs were obtained at monthly follow-up appointments until union was obvious at the osteotomy site and full weight bearing was possible. Follow-up was performed annually after the union had been determined. Radiographs, orthoroentgenographs, and medical records were evaluated by 1 researcher (F.Y.). Various examples of complications are shown in Figures 35 (Figures A,B,C,D,E,F, and G, available in the online version of the article).

Postoperative anteroposterior radiograph of the knee (A) and orthoroentgenograph (B) of a patient with a broken screw and conservative follow-up.

Figure 3:

Postoperative anteroposterior radiograph of the knee (A) and orthoroentgenograph (B) of a patient with a broken screw and conservative follow-up.

Postoperative anteroposterior radiographs of the knee of a patient with a nondisplaced lateral cortex fracture (A) and a patient with a displaced lateral cortex fracture (B).

Figure 4:

Postoperative anteroposterior radiographs of the knee of a patient with a nondisplaced lateral cortex fracture (A) and a patient with a displaced lateral cortex fracture (B).

Postoperative anteroposterior radiograph of the knee showing a patient with a displaced lateral plateau fracture (A). Postoperative anteroposterior radiograph of the knee showing that the patient had an early additional surgery for reduction and cannulated screw fixation (B). Anteroposterior radiograph of the knee obtained 4 years postoperatively showing that, due to irritation, implant removal was performed (C). Anteroposterior radiograph of the knee obtained 5 years postoperatively showing results of the total knee arthroplasty, which was performed due to severe knee pain and gonarthrosis (D).

Figure 5:

Postoperative anteroposterior radiograph of the knee showing a patient with a displaced lateral plateau fracture (A). Postoperative anteroposterior radiograph of the knee showing that the patient had an early additional surgery for reduction and cannulated screw fixation (B). Anteroposterior radiograph of the knee obtained 4 years postoperatively showing that, due to irritation, implant removal was performed (C). Anteroposterior radiograph of the knee obtained 5 years postoperatively showing results of the total knee arthroplasty, which was performed due to severe knee pain and gonarthrosis (D).

Radiographs of a patient with iliac crest fracture, early postoperative, and ten years postoperative.

Figure A.

Radiographs of a patient with iliac crest fracture, early postoperative, and ten years postoperative.

Radiograph of a patient with one subchondral and one intra-articular screw. (Left) Radiograph after early additional surgery. (Right)

Figure B.

Radiograph of a patient with one subchondral and one intra-articular screw. (Left) Radiograph after early additional surgery. (Right)

Orthoroentgenographs of a patient before (Left) and 12 years after MOWHTO (Right) demonstrating overcorrection. (Preoperative LTFA: 185°, postoperative LTFA: 164°)

Figure C.

Orthoroentgenographs of a patient before (Left) and 12 years after MOWHTO (Right) demonstrating overcorrection. (Preoperative LTFA: 185°, postoperative LTFA: 164°)

Radiographs of a patient with tibial tubercle fracture fixated with two screws intraoperatively, early postoperative (Left) and 11 years after MOWHTO (Right).

Figure D.

Radiographs of a patient with tibial tubercle fracture fixated with two screws intraoperatively, early postoperative (Left) and 11 years after MOWHTO (Right).

Orthoroentgenographs of a patient before (Left) and ten years after MOWHTO (Right) demonstrating under-correction. (Preoperative LTFA: 196°, postoperative LTFA: 180°)

Figure E.

Orthoroentgenographs of a patient before (Left) and ten years after MOWHTO (Right) demonstrating under-correction. (Preoperative LTFA: 196°, postoperative LTFA: 180°)

Radiographs and orthoroentgenograph of a patient with non-displaced LPF and conservative follow-up, early postoperative radiograph (Left), 13 years postoperative radiograph (Middle) and orthoroentgenograph (Right).

Figure F.

Radiographs and orthoroentgenograph of a patient with non-displaced LPF and conservative follow-up, early postoperative radiograph (Left), 13 years postoperative radiograph (Middle) and orthoroentgenograph (Right).

Orthoroentgenographs of a patient with 14 years follow-up.Preoperative LTFAs of right and left extremity were 183° and 188°, respectively. (Left)Two years after the first surgery, implant removal of right side and MOWHTO of left knee was performed. (Middle)Twelve years after right MOWHTO, LTFAs of right and left extremity were 170° and 180°, respectively. Note that despite the under-correction of the left side, the patient has been pain-free for both knees

Figure G.

Orthoroentgenographs of a patient with 14 years follow-up.

Preoperative LTFAs of right and left extremity were 183° and 188°, respectively. (Left)

Two years after the first surgery, implant removal of right side and MOWHTO of left knee was performed. (Middle)

Twelve years after right MOWHTO, LTFAs of right and left extremity were 170° and 180°, respectively. Note that despite the under-correction of the left side, the patient has been pain-free for both knees

Clinical and radiographic bone union criteria after MOWHTO were defined as load-dependent pain at the osteotomy site during walking and absence of radiologic evidence of progressive bony healing in combination with pain at the osteotomy site by physical contact.16 The modified version16 of the Radiographic Union Score for Tibial Fractures (RUST)17 was used to assess consolidation at the osteotomy site. The modified RUST gives points for each tibial cortex on anteroposterior and lateral views, excluding the anterior cortex on the lateral view due to the block of the fixation device. One point was given for no visible callus at the osteotomy line, 2 points if both the callus and the osteotomy line were visible at the same time, and 3 points for bridging the callus without a visible osteotomy line. The points of the 3 cortices are summed for a total modified RUST. The minimum score of 3 indicates that there is definitely no bone healing at the osteotomy line; a maximum score of 9 indicates definite osseous consolidation. Delayed union and nonunion are declared after 4 and 6 months, respectively.

Quadriceps stimulation and range-of-motion exercises were initiated on the first postoperative day. Toe-touch mobilization was provided with double crutches, and no brace was used during the postoperative period. Daily subcutaneous enoxaparin, 0.4 IU/mL, was administered during hospitalization and subsequently continued with 300 mg of oral acetylsalicylic acid after discharge. Partial load bearing was permitted after 6 weeks. Blood parameters including the erythrocyte sedimentation rate and C-reactive protein levels were determined on suspicion of infection, and lower extremity venous Doppler ultrasonographic examination was performed for deep venous thrombosis.

Statistical analysis was performed with SPSS, version 16.0, software (SPSS Inc, Chicago, Illinois). Descriptive statistics were computed and summarized; continuous variables were summarized using means, and categorical variables were summarized using proportions. Chi-square and analysis of variance (ANOVA) tests were used for comparison of discrete variables. Independent t test was used for comparison of continuous variables. The Kaplan–Meier method was used to calculate survival. The log-rank test was performed to compare the survival in MOWHTOs with and without complication. The Kaplan–Meier method demonstrates the estimation of survival probability of the remaining subjects for a special event and is commonly used for mortality studies but can be used for the estimation of the failure or revision of an implant, as was done for arthroplasty in this study. Confidence intervals were set at 95%, and values were considered statistically significant at P<.05.

Results

The outcomes of MOWHTOs that were performed on 504 knees in 441 patients at the authors' hospital between 2000 and 2010 were evaluated retrospectively. A total of 339 Puddu plates, 41 Anthony plates, and 124 Esenkaya L-type plates were used. The 63 additional knees represented bilateral operations. Mean follow-up was 117.7±26.3 months. Mean age of the study population was 52.6±7.0 years. Fifty-six (11.1%) knees were from men and 448 (88.9%) knees were from women. The 10-year joint survival rate was 94.8%.

In this study population, the total number of complications was 493; at least 1 complication was observed following 323 (63.7%) of the 504 MOWHTO operations, with at least 2 complications following 116 operations (23%). The number of MOWHTOs with grade 1, 2, and 3 complications were 294 (58.4%), 91 (18.1%), and 108 (21.5%), respectively. The number of MOWHTOs with grade 3 major complications requiring additional surgery was 102 (20.3%). The number of MOWHTOs with serious complications requiring additional surgery was 13 (2.6%). The observed complications are presented in Table 1.

Complications Associated With 504 Medial Open-Wedge High Tibial Osteotomiesa

Table 1:

Complications Associated With 504 Medial Open-Wedge High Tibial Osteotomies

Normal bone healing occurred following 88.7% of MOWHTOs, with an overall mean union time of 3.47 months (Table 2). The MOWHTOs were performed without grafts in 332 operations, and the overall mean correction angle was 11.4° (Table 3). The planned correction (range, 165°–174°) was achieved following 380 (75.4%) MOWHTOs (Table 4).

Types of Union and Mean Time to Union Following 504 Medial Open-Wedge High Tibial Osteotomies

Table 2:

Types of Union and Mean Time to Union Following 504 Medial Open-Wedge High Tibial Osteotomies

Mean Correction Angle (∆ Lateral Tibiofemoral Angle)a and Mean Time to Union With or Without Graft Use

Table 3:

Mean Correction Angle (∆ Lateral Tibiofemoral Angle) and Mean Time to Union With or Without Graft Use

Correction Type and Mean Angles Following 504 Medial Open-Wedge High Tibial Osteotomies

Table 4:

Correction Type and Mean Angles Following 504 Medial Open-Wedge High Tibial Osteotomies

Statistically significant relationships were observed between the following: LCF and additional surgery (chi-square test, P=.017); LCF and delayed union and nonunion (ANOVA test, P<.001); LCF and union time (independent t test, P=.000); and LCF and lateral crural hypoesthesia (chi-square test, P=.004). The authors found evidence that MOWHTOs with LCF are inclined to have resurgery and demonstrate lateral crural hypoesthesia and union problems. Statistically significant relationships were also observed between the following: graft use and mean correction angle (∆LTFA; independent t test, P=.000) and graft use and MOWHTOs associated with greater than 10° correction (chi-square test, P=.000). The authors found evidence that surgeons tend to use grafts as the correction angle increases (Table 3).

No statistically significant relationships were observed between graft use and union time (independent t test, P=.063) and between graft use and union type (normal, delayed union, and nonunion; ANOVA test, P=.440). The authors found no evidence that graft use decreases the risk of union problems.

No statistically significant relationships were observed between plate type (Puddu, Esenkaya, and Anthony) and union time (ANOVA test, P=.659), union type (ANOVA test, P=.359), and complication (chi-square test, P=.212). The authors found no differences between the 3 implants in terms of complication and union problems. In addition, no statistically significant relationships were observed between broken screws and additional surgery (chi-square test, P=.965).

The total number of arthroplasties was 27. More than half (n=14) were performed within the sixth to eighth years (Figure H, available in the online version of the article).

Distribution of the number of arthroplasties performed in each year of follow-up.

Figure H.

Distribution of the number of arthroplasties performed in each year of follow-up.

The Kaplan–Meier analysis demonstrated a cumulative survival of 94.8% at 120 months and a MOWHTOs survival rate of 94.4% with complication, 95.0% without complication, and 94.6% overall. The difference between MOWHTOs with and without complication was not statistically significant (log-rank test, P=.879; Kaplan–Meier analysis; Figures I and J, available in the online version of the article).

Kaplan Meier analysis.The Kaplan-Meier analysis demonstrated a cumulative survival of 94.8% at 120th month.

Figure I.

Kaplan Meier analysis.

The Kaplan-Meier analysis demonstrated a cumulative survival of 94.8% at 120th month.

Kaplan Meier analysis.The Kaplan-Meier analysis demonstrated a survival rate of 94.4% in MOWHTOs with complication, 95.0% without complication, and overall 94.6%. This difference between MOWHTOs with and without complication was not statistically significant. (Log-rank test, p=0.879

Figure J.

Kaplan Meier analysis.

The Kaplan-Meier analysis demonstrated a survival rate of 94.4% in MOWHTOs with complication, 95.0% without complication, and overall 94.6%. This difference between MOWHTOs with and without complication was not statistically significant. (Log-rank test, p=0.879

Discussion

Despite the high overall complication rate (63.7%) and complications requiring additional surgery (20.3%), the low rate of additional surgery for serious complications (2.6%) as well as the high 10-year joint survival (94.8%) and overall survival (94.6%) rates indicate that MOWHTO was a feasible solution in terms of procrastination of arthroplasty during this 10-year period.

The MOWHTO is effective in young patients (<55 years) and in those with early-stage medial varus gonarthrosis and is a valid treatment option despite the rapid development of arthroplasty in the past two decades.18 The MOWHTO can delay the need for arthroplasty.19 Reported 5-year survival rates for MOWHTO are between 75% and 95%, and 10-year survival rates are between 51% and 98%.20–26 The overall survival rate might have been high (94.6%) in this specific cohort relative to others because joint survival was assessed only by the requirement for arthroplasty excluding death. All deceased patients were excluded. In addition, this improved result compared with other studies was possibly related to the difference in body habitus, culture, and lifestyle between study populations, which requires further study.

The most appropriate age for HTO is a subject of debate, but it has been reported that the younger the patient, the better the long-term results.24,27–36 However, some authors agree that there is no difference in survival rate and pain relief according to age.37–40 Furthermore, Langlais and Thomazeau41 have shown that patients older than 70 years can also have successful results. Nagel et al42 stated that patients' activity level is the best predictor of the postoperative outcome. In addition to the report from Nagel et al,42 the current authors believe that orthopedic surgeons should focus on patients' biologic (physiologic) age and physical fitness status rather than their chronologic age, similar to the opinion of others.30,35,40,43–45 An older patient may have a higher activity level (eg, a retired, 70-year-old tennis player continues the sport to train young athletes) than a younger one, which makes the older patient's biologic age and physical fitness status superior.

In the literature, various models and studies have examined biologic age and physical fitness status, but there is no consensus or established protocol.46–57 There is a need for a biologic age and physical fitness status scoring system, especially for orthopedic patients, to determine the ultimate surgical approach for patients in the gray zone—those who are candidates for several surgical interventions, such as HTO and unicompartmental knee arthroplasty (UKA). Currently, because no consensus-established biologic age and physical fitness scoring system is available, this preference depends on the surgeon's surgical experience and the patient's postoperative expectation.

Reported complication rates following MOWHTO range from 1.9% to 55%,7 depending on the number of parameters studied as complications. As the number of examined parameters increases, the overall complication rate increases. Most of the complications do not require additional surgery and do not cause additional morbidity on long-term follow-up.8

In the current series, complications occurred following 63.7% of the MOWHTOs; for 20.3% of the MOWHTOs, the complications necessitated additional surgery. The general complication rate (63.7%) might have been high in this study because of the high number of complications examined. Despite being a grade 3 major complication, when patients who underwent additional surgery due to plate irritation (17.7%) were excluded, serious complications requiring additional surgery occurred following 2.6% of the MOWHTOs. This finding indicates that new-generation (lower profile) implants are needed to decrease the additional surgery rate.

The previously reported incidence of LCF following MOWHTO ranged from 0.3% to 34%.12,58–63 The LCF was the most common grade 1 complication in the current patient population and was associated with 33.1% of MOWHTOs, although LCF with a displacement of 2 mm or greater was associated with only 3.8% of MOWHTOs. The LCF was associated with delayed union and nonunion, lateral crural hypoesthesia, and revision (additional) surgery (P<.024). Therefore, disruption of the lateral cortex should be avoided.

In the authors' clinic, revision (additional) surgery is performed after the ninth month in cases of nonunion following MOWHTO because the current authors have observed bone healing and union at the osteotomy site up to 9 months. Among the 10 instances of nonunion that were recorded with LCF, only 2 did not heal by the end of the ninth postoperative month. In both of these cases, because of the development of deep infection, implant removal was performed along with an Ilizarov external fixator for revision. The other 8 patients had bone union by 9 months without requiring revision surgery. Only 1 instance of nonunion occurred in the absence of LCF, and it was associated with bone union at 7 months.

The rate of undercorrection associated with MOWHTOs in the current study was 20.6%. This was similar to the 20% reported by Koshino et al25 in a study of closed-wedge osteotomy with a target of 10° of anatomic valgus correction, as well as the 20% reported by Hernigou and Ma64 in a study of MOWHTO with a target of 3° to 6° of mechanical valgus correction.

The HTO carries a risk for undercorrection, as observed in case series involving experienced surgeons regardless of whether it is performed as an open or closed wedge.64 In the current series, the mean postoperative LTFA of patients with undercorrection was 176.4°. Therefore, the current authors found that 3° or greater of correction is required in preoperative planning to avoid varus (>174°) malalignment in patients with undercorrection. To achieve the desired LTFA between 165° and 174°, an LTFA between 162° and 171° should be targeted. At 4%, the rate of overcorrection in the current series was also similar to that reported previously.64

Many factors, including LCF, graft use, implant type, and smoking, have been suggested to affect union after MOWHTO.16,65,66 In addition, opinions differ regarding what constitutes the normal timing of union. For example, delayed union has been defined as the presence of pain at the osteotomy site after 45 days (with evidence of loss of correction before union), with nonunion defined as the absence of radiologic union (complete filling of the osteotomy line) requiring iliac crest bone grafting.64 However, delayed union has also been defined as a union time greater than 3 months.67

In the authors' clinic, delayed union is considered to be union occurring after 4 months, and nonunion is defined as a lack of union after 6 months, as also described elsewhere.68 In cases of non-union in their clinic, as elsewhere,13 the current authors wait up to 9 months before performing revision surgery after MOWHTO because they have seen bone healing up to this time. With this limit, the current authors observed delayed union and nonunion in 9.1% and 2.2% of MOWHTOs, respectively. In a study of 182 patients, Warden et al67 reported delayed union and nonunion after MOWHTO of 6.6% and 1.6%, respectively.

No statistically significant difference was found between operations with or without graft application (with iliac wing tricortical grafts) in terms of the time of union or union type (normal, delayed union, nonunion; P=.540). However, a statistically significant relationship was found between graft use and correction angle (P=.021). The rate of graft use was significantly higher for MOWHTOs associated with greater than 10° correction than for those with 10° or less correction (P=.000). Notably, the currently available evidence in the literature is not sufficient enough to strongly support the superiority of MOWHTO with bone graft to MOWHTO without bone graft in terms of union.69

Given this information, the authors believe that there is a tendency for surgeons to use grafts as the correction angle (∆LTFA) increases (especially over 10°), even though the graft use does not contribute to the bone union (union time or union type). Shortly, the most important factor in graft use is the surgeon's preference.

In addition, a statistically significant difference was observed in terms of union type (normal/delayed/nonunion) or union time between the operations resulting in correction (∆LTFA) of greater than 10° compared with 10° or less (P=.017). However, this difference was not clinically important because mean union time was 3.55 months for MOWHTOs associated with greater than 10° correction and 3.39 months for those with 10° or less correction, meaning the difference between them was 0.16 month or approximately 5 days.

The authors observed no statistically significant differences in terms of normal union, delayed union, nonunion, union time, or complications between the 3 types of plates used for MOWHTO (P=.067). This is the first study comparing the Esenkaya L plate and the Anthony plate with the Puddu plate in terms of complications. However, the current study did not investigate all complications mentioned in the literature.

In the current study, LPF was observed in 21 (4.2%) instances, which compares with previously reported rates of 11.7%,70 1.93%,12 and 2.17%.7 Two patients in the current study underwent additional surgery as a result of a displaced LPF, and 1 of these individuals had delayed union.

The authors observed a superficial infection (cellulitis) rate of 2.0% (for which treatment was local wound care with oral antibiotherapy), and a deep infection rate of 1.6% (treated by implant removal with debridement, with or without an Ilizarov fixator for infected nonunion). Reported general infection rates following MOWHTO vary between 0.5% and 10%,71–73 with superficial infection rates of 1% to 9% and deep infection rates of 0.5% to 4.7%.74

Deep venous thrombosis occurred following 4 (0.8%) MOWHTOs in the current study, similar to the literature.75 In each case of deep venous thrombosis, the patient healed within 6 months with the use of oral anticoagulants. One patient had an iliac wing fracture during autologous graft harvesting and was treated conservatively. Chae et al7 reported 3 iliac wing fractures among 138 patients, and all were treated conservatively. Nocini et al76 reviewed the literature focusing on fractures of the iliac crest and found 24 fractures related to bone harvesting from the anterior region and 12 from the posterior region.

In 3 instances of the occurrence of tibial tubercle fractures during osteotomy in the current study, additional fixation was performed with anteroposterior-oriented screws in the same session. Knee flexion was gradually increased until union was achieved by application of a hinged-angle brace. The current study is the first study reporting tibial tubercle fracture during MOWHTO.

In the current study, implant removal due to plate irritation was the second most common complication, with 89 (17.7%) instances, which is comparable to previously reported frequencies of 7% to 60%.13,77 Additional surgery was also performed in 13 (2.6%) instances in the current study due to other grade 3 complications. One early revision was made due to an intra-articular screw, and 2 revisions resulted from displaced LPFs. Eight implant removals followed a deep infection, 1 revision resulted from implant failure, and 1 vascular repair was performed with saphenous vein grafts at 3 months because of the development of pseudoaneurysm as a result of iatrogenic damage to the adventitia layer of the popliteal artery. By comparison, a previously reported rate of additional surgery was 3%.8

Among other grade 3 complications in the current study, 1 incidence of tibial nerve neuropraxia was recorded. During the postoperative period, the patient had hypoesthesia on the heel and the medial side of the sole of the foot, but reported no motor loss and then recovered within 1 year with conservative follow-up. This is the second case of tibial nerve neuropraxia reported in the literature.78

Lateral crural hypoesthesia was observed in 5 patients who had not recovered by the last follow-up observation. In all 5 patients, LCF occurred during the operation. Therefore, the occurrence of lateral crural hypoesthesia may have been the result of LCF and stretching of the peroneal nerve during the correction. Although peroneal paresis was initially thought to occur only in closed-wedge HTO,79,80 evidence now indicates that this complication may also occur in MOWHTO.9

In the current study, implant failure (broken screw) occurred in 3 cases during follow-up, resulting in 1 revision for loss of correction. This is similar to the study by Chae et al7 in which 6 of 138 knees had broken screws, 1 of which had significant loss of correction.

The Kaplan–Meier analysis demonstrated that the difference between MOWHTOs with and without complication was not statistically significant in terms of joint survival; however, from the viewpoint of the patient or his or her physician, the development of even the smallest complication is clinically important.

According to the current study, MOWHTO seems to have a higher complication rate compared with its successor, UKA, but this is consistent with the literature because more complications were observed after HTO.81–88 In the literature, 4 meta-analyses compared HTO and UKA.89–92 In their meta-analysis, Zhang et al89 reported that the ratio for an excellent outcome was higher and the risks of revision and complications were lower in UKA than in HTO. Likewise, Brouwer et al91 concluded that there is a high level of evidence that HTO causes more complications than UKA, and Griffin et al92 reported more complications after HTO. Despite these findings, Fu et al90 reported no significant difference between UKA and HTO in terms of revision risk and complication. However, most of the articles reported in the literature were about closed-wedge HTO.93 To summarize the issue, the literature is still controversial regarding the complications of UKA and HTO. In addition, there is an increasing trend in the use of UKA.44

The strengths of this study were the large number of MOWHTOs that were included, the long follow-up period, the examination of an isolated group of patients, the exclusion of patients with concomitant surgeries, the evaluation of under- and overcorrection, the assessment of joint survival only when there was a requirement for arthroplasty (exclusion of the deceased), and the inclusion of union time and graft use. The limitations of this study were that sagittal-plane deformities, range of motion, stiffness, clinical outcomes, age, sex, body mass index, smoking, differences in surgical technique (grafts, implants), and loss of correction (excluding loss resulting from implant failure) were not examined. The main weakness of the study was its retrospective nature.

The outcomes reported are similar to those from other studies. In terms of clinical approach, the authors suggest two changes: delaying additional surgery for nonunion cases without infection after MOWHTO to the end of the ninth month and targeting LTFA between 162° and 171° in preoperative planning to avoid undercorrection.

Disruption of the lateral cortex should be avoided. Graft use is at the surgeon's discretion regardless of union time. As the mean correction angle (∆LTFA) increases, surgeons tend to use grafts, especially when the mean correction angle is over 10°. Tibial tubercle fracture may occur in MOWHTO. Further study is required to explain the difference in survival after MOWHTO for different study populations. New-generation (lower profile) implants are needed to decrease the rate of additional surgery.

Conclusion

Although the overall complication rate and the need for additional surgery were high, the need for additional surgery because of serious complications was low following MOWHTO. The 10-year survival rate was 94.8%, indicating that this approach can be safely applied for patients with isolated medial gonarthrosis.

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Complications Associated With 504 Medial Open-Wedge High Tibial Osteotomiesa

Complication GradeRate (%)No.
Grade 1 minor
  Total58.4294
  LCF33.1167
    Displaced LCF (complete union in ≤9 months)3.819
  Undercorrection20.6104
  Overcorrection4.020
  Broken screw (conservative follow-up)0.42
  Iliac crest fracture0.21
Grade 2 moderate
  Total18.191
  Delayed union9.146
  Nondisplaced LPF (conservative follow up)3.719
  Superficial infection (cellulitis)2.010
  Nonunion (healed between the end of sixth and ninth months)1.89
  DVT0.84
  Tibial tubercle fracture0.63
Grade 3 major
  Total21.5108
  Implant removal because of irritation17.789
  Deep infection1.68
    A. Implant removal and debridement alone1.26
    B. Implant removal/debridement with an Ilizarov fixator for infected pseudoarthrosis0.42
  Lateral crural hypoesthesia1.05
  Additional surgery for displaced LPF0.42
  Tibial nerve neuropraxia0.21
  Iatrogenic popliteal artery injury0.21
  Intra-articular screw0.21
  Broken screw with implant failure requiring additional surgery0.21
  Grade 3 major complications requiring additional surgeryb20.3102
  Serious complications requiring additional surgeryc2.613

Types of Union and Mean Time to Union Following 504 Medial Open-Wedge High Tibial Osteotomies

Bone HealingNo. (%)Mean Time to Union, mo
Normal (0–4 mo)447 (88.7)3.17
Delayed union (5–6 mo)46 (9.1)5.26
Nonunion (≥7 mo)11 (2.2)8.50
Total5043.47

Mean Correction Angle (∆ Lateral Tibiofemoral Angle)a and Mean Time to Union With or Without Graft Use

Graft UseNo.Mean Correction AngleMean Time to Union, mo
With graft17213.2°3.21
Without graft33210.5°3.61
Total50411.4°3.47

Correction Type and Mean Angles Following 504 Medial Open-Wedge High Tibial Osteotomies

Correction (Lateral Tibiofemoral Angle)No. (%)Mean Anglea
Undercorrection (>174°)104 (20.6)176.42°
Achieved the planned correction (165°–174°)380 (75.4)170.70°
Overcorrection (<165°)20 (4.0)162.80°
Total504171.57°
Authors

The authors are from the Department of Orthopedics and Traumatology (FY, USA, MC, MCA, AK, EU, AIB, MAK), Metin Sabanci Baltalimani Bone Diseases Education and Research Hospital, and the Department of Family Medicine (DM-C), Marmara University Pendik Education and Research Hospital, Istanbul, Turkey.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Furkan Yapici, MD, Department of Orthopedics and Traumatology, Metin Sabanci Baltalimani Bone Diseases Education and Research Hospital, Baltalimani cayir st 34470 sariyer, Istanbul, Turkey ( furkanyapici@hotmail.com).

Received: February 22, 2019
Accepted: June 11, 2019

10.3928/01477447-20200819-01

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