Total knee arthroplasty (TKA) is a much-needed and highly successful surgical procedure.1,2 The number of TKAs performed is projected to continue to rise as the population older than 65 years in the United States grows and as an increasing number of younger patients are considered for TKA.3–5 As TKA continues to evolve and become further refined, new products are continually being introduced into the market. Many of these products are intended to further improve patient outcomes and reduce performance outliers. One such technology is custom instrumentation (CI) for TKA.
Custom instrumentation offers an alternative technique to conventional TKA. However, CI costs both the patient and the health care system time and money.6–8 In the current health care environment, new technologies must be vetted and justified with proven clinical and value-based advantages.
Multiple authors have reported on CI vs conventional TKA, and these findings have been conflicting. Because CI does not breech the intramedullary canal, it is hypothesized that CI may have reduced blood loss, resulting in less requirement for transfusion.9,10 Some authors have reported similar transfusion rates, whereas others have found reduced rates with CI TKA.10–25 Some authors have also reported differing findings regarding length of stay (LOS) between CI and conventional TKA.11,17,19,24,26 Additionally, some authors have shown a reduction in operative time with CI TKA, whereas others have not.7,8,11,12,15,17,19,24–31 Finally, there have been no previous reports on the difference in discharge destination between these groups. Given the nature of the varied conclusions in the literature, the current authors were motivated to report their own findings.
The goal of this study was to expand on the work of others, particularly where controversy existed, by retrospectively comparing TKA performed with CI vs conventional intramedullary instrumentation. Specifically, the authors aimed to evaluate for a difference in multiple quality metrics, including transfusion rate, operative time, deep venous thrombosis/pulmonary embolism (DVT/PE) rate, LOS, discharge destination, and 30-day surgical site infection, in patients undergoing elective TKA.
Materials and Methods
Institutional review board approval was obtained. Data from 231 consecutive patients meeting the inclusion criteria and undergoing CI TKA were collected. No patients were lost to follow-up. Using propensity score matching for age, sex, and body mass index in SPSS version 22.0 software (IBM, Armonk, New York), the authors matched 231 patients who underwent conventional TKA to 231 patients who underwent CI TKA between February 1, 2012, and May 1, 2016. Patients older than 18 years with end-stage osteoarthritis undergoing primary TKA were included. Patients with previous osteotomies, retained hardware, or previous fracture were excluded. There was no exclusion for body mass index. Patients underwent TKA performed by 1 of 2 fellowship-trained joint surgeons. Conventional and CI TKA were all performed with the same GMK Sphere implant (Medacta, Castel San Pietro, Switzerland). Conventional TKA was performed with a standard intramedullary femoral guide and an extramedullary tibial guide. The MyKnee (Medacta) computed tomography–based femur and tibia system was used for all CI TKAs. All TKAs were performed with the same protocol, involving a tourniquet, which was deflated at the time of skin closure; a single hemovac drain; a weight-based dose of intravenous tranexamic acid just prior to incision; a dose of intravenous tranexamic acid at the time of skin closure; and the same postoperative anticoagulation protocol (an enoxaparin sodium bridge to warfarin sodium for 21 days). The same standard protocol for transfusion was applied to both groups, regardless of surgical technique. The same physical therapists and rehabilitation protocols were used for both groups.
The authors matched 231 conventional TKAs to 231 consecutive CI TKAs using the propensity score matching function in SPSS for age, sex, and body mass index. The differences in categorical variables were analyzed using Pearson's chi-square test. Continuous data were analyzed with a 2-sample Student's t test. Fisher's exact test was used to evaluate differences in PE and DVT. Statistical significance was set at P≤.05. Based on previously reported data on LOS, a power analysis (P=.80) determined that a minimum of 108 patients were required to detect a significant difference (α=0.05, 2-sided significance level) of 0.7 days between groups.17 An enrollment target of 200 patients was selected.
A total of 231 propensity score matched patients were included in the conventional TKA group, and 231 consecutive patients were included in the CI TKA group. There was no significant difference in age, sex, body mass index, or preoperative hemoglobin between the groups (Table 1).
In-Hospital Postoperative Data
In-hospital data for the immediate postoperative period from the post-anesthesia care unit and postoperative day 0 and day 1 data from the hospital floor were collected and analyzed (Table 2). There was no difference in immediate postoperative temperature (P=.18), heart rate (P=.86), respiratory rate (P=.65), or systolic (P=.22) or diastolic (P=.99) blood pressure between groups. There was no difference in postoperative day 0 and day 1 minimum oxygen saturation, maximum temperature, or visual analog scale pain score (all P>.05) between groups. Hemovac output was similar between groups on postoperative day 0 (176 mL conventional vs 175 mL CI; P=.93).
In-Hospital Postoperative Data
There was no significant difference in discharge hemoglobin (P=.74) or hemoglobin drop (P=.17) between the groups (Table 3). Hemoglobin drop was defined by the difference between preoperative hemoglobin and discharge hemoglobin. There was no significant difference in transfusion rate (P=.69). Operative time was 102 minutes in both groups (P=.84). Length of stay was 2.6 days in the conventional group and 2.5 days in the CI group (P=.43). Two patients in each group were diagnosed with a PE in the first 30 days after surgery (0.86% incidence rate). One patient in the conventional group and 2 patients in the CI group were diagnosed with DVT (P=1.00). Compared with the CI group, patients undergoing conventional TKA were just as likely to be discharged to home vs to a rehabilitation facility (83% vs 82% home; 17% vs 18% rehabilitation; P=.90). No patient in either group developed a surgical site infection in the first 30 days after surgery.
Total knee arthroplasty is a much-needed and highly successful surgical procedure.1,2 Custom instrumentation TKA is one alternative technique to conventional TKA. Although multiple studies have been published on this topic, controversies remain. The current authors' goal was to provide a large, retrospective, propensity score matched analysis evaluating for differences in the first 30 postoperative days between CI TKA and conventional instrumentation in TKA. Specifically, they evaluated transfusion rate, operative time, DVT/PE rate, LOS, and discharge destination for patients undergoing elective TKA.
Reported transfusion rates have varied between CI and conventional TKA, with some authors reporting similar rates and others reporting a reduced transfusion rate with CI TKA.10–18,24,27,31 Similar to CI, computer-assisted surgery in TKA does not violate the intramedullary canal. Therefore, computer-assisted surgery could also be expected to be associated with a lower transfusion rate. However, mixed transfusion rates have been reported for computer-assisted surgery as well.20–22 In the current analysis of 231 patients with CI TKA and 231 patients with conventional TKA, no difference in transfusion rate or postoperative hemoglobin drop was found. The preoperative patient demographics were nearly identical regarding age, sex, and body mass index. There was also no difference in pre-operative hemoglobin between groups.
Various results have been reported regarding LOS in conventional vs CI TKA. Boonen et al11 investigated 180 patients and found no difference in LOS; however, Vide et al17 reviewed 95 patients and found a one-half day reduction in LOS. Other authors had similar findings.11,17,24,26 In the current evaluation of 462 patients, no difference in LOS was found.
Multiple authors have evaluated operative time in CI TKA. Nunley et al7 found a 12-minute reduction in operative time with 114 total patients. Chareancholvanich et al12 found a 5-minute reduction in operative time with 80 patients. Some authors have reported up to a 30-minute reduction in operative time.7,8,11,12,15,17,24–26,28–30 However, the current study of 462 patients showed no reduction in operative time between groups. This study was completed at an academic institution, and this may have implications for operative time, potentially obscuring the time savings generally associated with a CI system.
To the authors' knowledge, discharge disposition for conventional vs CI TKA has not been previously reported. They hypothesized that, compared with CI TKA, conventional TKA would be associated with increased pain, blood loss, or transfusion rates, leading to increased LOS or more patients requiring admission to rehabilitation facilities. However, the authors did not identify any difference in these outcomes or in discharge disposition between the groups. Nearly identical numbers of patients in their group of 462 patients met discharge criteria for home vs to a rehabilitation facility (82% vs 83% discharged home; P=.90).
This study had several limitations. Rates of PE and DVT were low in both groups, so this study was likely under-powered to assess a difference in these 2 specific complications. Additionally, because this study was performed in an academic setting with longer operative times as compared with a private setting, much of the reduction in operative time that is typically seen with CI may have been obscured. Further, although propensity score matching attempts to mitigate confounding variables, it is not as powerful as a blinded, randomized control study. Finally, cost analysis, radiographic analysis, and patient-reported outcomes were not included because they were not objectives of this study. However, other authors have reported on these factors.
Compared with TKA having conventional instrumentation, CI TKA did not reduce operative time, transfusion rate, postoperative hemoglobin drop, hemovac output, or hospital LOS. Custom instrumentation TKA did not alter discharge disposition or reduce the rate of discharge to a rehabilitation facility. The authors did not identify any difference between CI and conventional TKA for the factors they examined in their review of 231 patients vs 231 propensity score matched controls.
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|Conventional TKA (n=231)||CI TKA (n=231)|
|Sex, No. (%)||1.00|
| Female||146 (63)||146 (63)|
| Male||85 (37)||85 (37)|
|Age, mean, y||68.7||68.6||.92|
|Body mass index, mean, kg/m2||31.8||31.9||.91|
|Preoperative hemoglobin, mean, g/dL||12.43||12.34||.49|
| Obstructive sleep apnea||91||91||1.00|
| Chronic obstructive pulmonary disease||26||25||.88|
In-Hospital Postoperative Data
|Conventional TKA (n=231)||CI TKA (n=231)|
| Temperature, mean, °F||95.9||96.3||.18|
| Heart rate, mean, beats per minute||80.9||79.6||.86|
| Respiratory rate, mean, breaths per minute||17.5||17.4||.65|
| Systolic blood pressure, mean, mm Hg||136.0||133.0||.22|
| Diastolic blood pressure, mean, mm Hg||68.0||68.0||.99|
|Postoperative day 0|
| Minimum oxygen saturation, mean||93.1%||93.1%||.96|
| Maximum temperature, mean, °F||98.1||98.0||.17|
| Hemovac output, mean, mL||176.4||175.0||.93|
| VAS pain score, mean||2.3||2.1||.12|
|Postoperative day 1|
| Minimum oxygen saturation, mean||92.5%||93.3%||.15|
| Maximum temperature, mean, °F||99.0||99.0||.40|
| Hemovac output, mean, mL||73.2||109.2||.01|
| VAS pain score, mean||3.6||3.4||.20|
|Conventional TKA (n=231)||CI TKA (n=231)|
|Preoperative hemoglobin, mean, g/dL||12.4||12.3||.49|
|Discharge hemoglobin, mean, g/dL||10.3||10.4||.74|
|Hemoglobin drop, mean, g/dLa||2.1||1.9||.17|
|Red blood cell transfusions, No.||1 (0.43%)||4 (1.70%)||.69|
|Operative time, mean, min||102.0||102.0||.84|
|Length of stay, mean, d||2.6||2.5||.43|
|Venous thromboembolism events, No.|
| Pulmonary embolism||2 (0.86%)||2 (0.86%)||1.00|
| Deep venous thrombosis||1 (0.43%)||2 (0.86%)||1.00|
|Discharge disposition, No.|
| Home||190 (82%)||191 (83%)||.90|
| Subacute rehabilitation||41 (18%)||40 (17%)||.90|
|30-day surgical site infection, No.||0||0|