Feature Article 

Immediate Weight Bearing After Cementless Total Hip Arthroplasty

Charles J. Taunt Jr., MD; Henry Finn; Patricia Baumann

  • Orthopedics
  • March 2008 - Volume 31 · Issue 3

Abstract

This study analyzed 399 Balance femoral stems to determine whether immediate full weight bearing following total hip arthroplasty affected radiographic osseointegration. Postoperatively, all patients were permitted unlimited weight bearing. Findings demonstrated osseointegration was successful in 99.5% of femoral components. Of these, 0.5% subsided in the first 6 postoperative weeks and then osseointegrated; 0.5% failed to osseointegrate. Patients with Dorr C bone had a significantly increased rate of subsidence (P=.006). These findings indicate the Balance stem reliably osseointegrates without subsidence in patients with Dorr A or B bone, despite immediate full weight bearing.


Cementless femoral stem implantation has become a reliable technique that yields excellent results in selected patients undergoing total hip arthroplasty (THA).1-3 As stem designs and biomaterials have evolved, many cementless femoral stems have proved effective and reliable. With regard to rehabilitation, a period of initial protected weight bearing has remained the standard for cementless femoral stems.4,5 Avoiding micromotion to allow bone ingrowth prior to weight bearing has been advocated for prevention of implant subsidence and for avoiding fibrous ingrowth at the bone-implant interface.6-13

Only 2 published studies have addressed the effect of immediate postoperative full weight bearing on the outcome of THA and its effect on femoral stem osseointegration.5,14 In both studies, weight bearing was allowed out of necessity because of simultaneous bilateral THA. Rao et al5 demonstrated increased subsidence but no effect on femoral osseointegration in a small cohort of patients (28 hips in 14 patients) with the use of the Taperloc stem (Biomet Inc, Warsaw, Indiana). Ritter et al14 reviewed a series in which a wide variety of prosthetic designs were implanted, and they concluded fit and fill were the most important for obtaining stability and femoral osseointegration. They reported a 3.3% (6 of 184) femoral component aseptic loosening rate, which was higher than would generally be expected. These authors attributed their cases of aseptic loosening to poor fit and fill.

This study prospectively analyzed the clinical and radiographic results of 399 (337 patients) cementless titanium tapered femoral stems with anatomic proximal geometry for optimal fit and fill to determine whether immediate full weight bearing affected radiographic osseointegration or clinical function. The study hypothesis was the design of this femoral component would allow immediate full weight bearing and successful osseointegration without subsidence would be obtained. All patients were permitted unlimited full weight bearing on the first postoperative day. Engh radiographic criteria for stable fixation15-19 and the Harris hip score (HHS)20,21 were used for defining a successful outcome.

Materials and Methods

We believed the prosthetic design feature that was critical to successfully allowing immediate full weight bearing was optimal fit and fill of the proximal femur. Thus, a 3° tapered stem was designed specifically to provide optimal fit and fill of the proximal femur, which we postulated would provide reliable osseointegration despite immediate full weight bearing. The proximal geometry of this stem was defined by the best approximation to the normal femoral anatomy based on an analysis of 1000 computed tomography (CT) scans that had been catalogued after the production of custom femoral implants by Biomet Inc. On this basis, it was established the sagittal plane of the proximal femur has a straight posterior contour but a consistent anterior flare. Noble et al22 described a similar proximal femoral geometry in an anthropometric study of 200 femora. The Balance femoral stem (Balance hip, Biomet Inc) incorporates the anterior flare, creating a side-specific implant, with near custom fit and fill of the proximal femur (Figure 1).

Figure 1: The implant incorporates the consistent anterior flare of the proximal femur

Figure 2: Two cross-sectional levels in proximal one-third of the femoral component were compared with fit and fill of a custom stem

Figure 1: The implant incorporates the consistent anterior flare of the proximal femur. Figure 2: Two cross-sectional levels in proximal one-third of the femoral component were compared with fit and fill of a custom stem.

To confirm the proximal fit and fill of this design, we compared the cross-sectional areas of this stem with that of custom CT-generated stems. One hundred femora were studied by use of CT image data that defined 3 levels of cortical density. Single anterorposterior and lateral cut planes along with 4 transverse sections of the proximal femur were reconstructed. Custom implants then were designed based on their intimate contact with medium-density bone (751-1350 Hounsfield units on CT) in the proximal third of the femur. Low-density bone (300-750 Hounsfield units) can be removed with a reamer or rasp and was not considered.

Balance hip templates were then overlaid on the custom stem design, and a comparison of proximal fit and fill of the femur was determined. The cross-sectional area of the Balance stem was determined at 2 transverse sections of the proximal femur (Figure 2) and was compared to the corresponding cross sections of the custom stem implant. The cross-sectional area of the custom stem served as the reference for the percentage of proximal femoral fit and fill of this component. The Balance stem achieved 88.5% of the fill of the custom stem proximally and 79.2% of the fill of the custom stem distally (Figure 3).

Figure 3: Graph comparing fit and fill for Balance and custom stems

Figure 3: Graph comparing fit and fill for Balance and custom stems.

From May 1994 through December 2002, a total of 399 Balance cementless femoral stems were implanted in 337 patients by the same surgeon. Sixty-two patients underwent bilateral procedures, of which 36 were simultaneous. Average patient age was 56 years (range, 15-86 years).

Preoperative diagnosis was symptomatic end-stage osteoarthritis in 285 hips. Other diagnoses included avascular necrosis (57 hips), developmental hip dysplasia (23 hips), post-traumatic arthritis (18 hips), rheumatoid arthritis (11 hips), prior septic arthritis (3 hips), and femoral-neck fracture (2 hips).

The Charnley classification and Dorr classification of proximal femoral anatomy were determined preoperatively and were recorded for use as independent variables.15,16,20,23 One hundred forty-seven patients were assigned Charnley class A, 199 were Charnley class B, and 53 Charnley class C. One hundred twenty-eight hips were Dorr class A, 254 were Dorr class B, and 17 were Dorr class C.

Preparation of the femur for implantation of the stem was accomplished with the use of sequential 1-mm 3° conical reamers. Component size was determined by the first reamer to obtain chatter in the femoral isthmus. The final reamer was advanced proximally, and all cancellous bone was removed from the proximal one-third of the femur, allowing intimate contact of the prosthesis with endosteal cortical bone. Broaches were used for finish preparation and as trial components.

Postoperative management included full weight-bearing ambulation on the day following surgery. Physical therapy was used for gait training, with assistive devices for balance only. Abductor-strengthening exercises were initiated on the second postoperative day. Patients were discharged with the assistive device most comfortable for them and were allowed to discontinue the aid according to their comfort.

Patients were evaluated clinically and radiographically preoperatively, 6 weeks and 3 months postoperatively, and then yearly thereafter, at which time Harris hip scores20,21 were recorded. All of the patients in the study were evaluated at each postoperative visit by the operating surgeon.

Immediate postoperative anteroposterior and lateral radiographs were obtained. These were repeated at 6 weeks and 3 months postoperatively, and then at annual examinations.

Radiographic assessment of biologic fixation as defined by Engh et al15 and modified by Ritter et al14 was based on evaluation of AP and lateral radiographs of the hip. To avoid any bias, each radiograph was evaluated by 2 of the authors, and the consensus was recorded as to osseointegration and stability, which were determined by the presence of both calcar atrophy and endosteal spot welds, as well as by the absence of both reactive lines and subsidence. When subsidence occurred, the distance subsided was determined with an electronic caliper by the average of the distance from the tip of the trochanter to the shoulder of the prosthesis as well as the base of the lesser trochanter to the most proximal aspect of porous coating on the prosthesis.

Results

Median follow-up was 2.5 years (interquartile range, 1.2-4 years; range, 1 month–8 years). Two hundred seventy-one hips (67.9%) were available for a minimum 2 years of follow-up, and 124 hips (31.1%) were available for 3 months to 2 years of follow-up. Four hips (1%) were lost to early follow-up (1 patient died and 3 patients were noncompliant).

Median time to latest follow-up in the 2-year cohort was 3.3 years (range, 2-8 years). Mean preoperative HHS was 47.3 (standard deviation [SD] 12.8; range, 6-81), and mean postoperative HHS was 88.1 (SD, 12.4; range, 34-100) (paired t test, P,.0001). Median time to latest follow-up in the <2-year cohort="" was="" 1="" year="" (range,="" 3="" months-2="" years).="" mean="" preoperative="" hhs="" was="" 44.1="" (sd,="" 13.7;="" range,="" 16-84),="" and="" mean="" postoperative="" hhs="" was="" 88.1="" (sd,="" 11.0;="" range,="" 30-100)="" (paired="">t test, P<.0001). there="" was="" no="" statistically="" significant="" correlation="" between="" hhs="" and="" age,="" sex,="" or="" charnley="" or="" dorr="" classification.="">

Figure 4A: An osseointegrated stem

Figure 4B: An osseointegrated stem

Figure 4: AP (A) and lateral (B) radiographs showing an osseointegrated stem.

Immediate postoperative radiographs were reviewed in all patients. Engh criteria15 as modified by Ritter et al14 for radiographic interpretation of biologic fixation were recorded at 3 months postoperatively and at the most recent follow-up. A total of 393 of 395 hips (99.5%) met the criteria for determination of osseointegration of a femoral component (Figure 4). A total of 391 hips (99%; 95% confidence interval, 97.4%-99.7%) were osseointegrated as shown radiographically, with no subsidence at the time of latest follow-up. Two hips (0.5%) subsided in the first 6 postoperative weeks but were osseointegrated at 3 months. Two hips (0.5%) became aseptically loose, subsided, and required subsequent revision. Two of 17 Dorr C hips (11.8%) subsided compared with 2 of 252 Dorr B hips (0.8%) and zero of 126 Dorr A hips (0%); this difference was statistically significant (Fisher’s exact test, P=.006). There was no statistically significant correlation between successful osseointegration and age, sex, or Charnley classification.

Two femoral components became aseptically loose and eventually went on to revision. The first of these was implanted after a resection arthroplasty for treatment of an infected Sugioka osteotomy and stage IV avascular necrosis in a 42-year-old man. This patient’s proximal femoral anatomy was abnormal (Figure 5). In retrospect, he would have been a better candidate for fixation in the isthmus with a cylindrical stem.

Figure 5A: Preoperative radiograph showing an infected osteotomy

Figure 5B: Postoperative radiograph showing reimplantation with the Balance stem

Figure 5: Preoperative radiograph showing an infected osteotomy (A). Postoperative radiograph showing reimplantation with the Balance stem (B).

The second failure occurred in a 38-year-old man who had osteoarthritis secondary to bilateral Legg-Calvé-Perthes disease as a child and a previous valgus-producing right intertrochanteric osteotomy (Figure 6) as well a subsequent bone-grafting procedure on the same hip. He underwent simultaneous bilateral THA. The femoral stem on the right side subsided within 6 weeks and went on to revision, and the left stem osseointegrated reliably without subsidence. This patient’s proximal femoral anatomy had been distorted both by his Legg-Calvé-Perthes disease and by a previous surgical intervention, and he also would have been a better candidate for femoral isthmus fixation.

Two femoral stems subsided within the first 6 weeks but osseointegrated reliably. The first of these was implanted in a 59 year-old woman with Dorr C bone during simultaneous bilateral THA for severe osteoarthritis. Her left femoral component had subsided 10 mm in the first 6 weeks postoperatively but was osseointegrated at 12 weeks, with stable osseointegration evident by 1 year postoperatively.

The second patient whose component subsided was a morbidly obese (body mass index, 62) 60-year-old woman with Dorr C bone who underwent THA for stage IV avascular necrosis. Her femoral component had subsided 11 mm at 6 weeks but was osseointegrated at 3 months, with stable osseointegration evident by 3 years postoperatively. In retrospect, we concluded the femoral component was undersized.

Figure 6A: A previous osteotomy and bone graft in a patient with Legg-Calvé-Perthes disease

Figure 6B: Postoperative radiograph showing the Balance stem after THA

Figure 6: Preoperative radiograph showing a previous osteotomy and bone graft in a patient with Legg-Calvé-Perthes disease (A). Postoperative radiograph showing the Balance stem after THA (B).

Discussion

There have been 3 reports of immediate weight bearing after cementless femoral stem implantation.5,14,24 The general consensus in reports on cementless THA has been to limit weight bearing postoperatively to avoid fibrous ingrowth and subsidence.4-13 No reports of a prosthesis specifically designed for immediate full weight bearing postoperatively have been published previously.

Cementless stems have been used successfully in young, active patients and can equal the good results obtained historically with cemented stems.3,25-27 A disadvantage of cementless stems has been the lack of sufficient initial stability to allow full weight bearing in the immediate postoperative period. Fibrous ingrowth may occur and may be accelerated by early weight bearing.6,7

As a result, patients undergoing cementless THA routinely are allowed protected weight bearing for up to 6 weeks or until osseointegration has been identified radiographically.4,5 This period of protected weight bearing can delay the rehabilitative phase of THA and potentially increase complications and cost.24 Patients with bilateral joint disease also are at a disadvantage with present cementless designs because a limited weight-bearing protocol is not practical for patients undergoing simultaneous THA.5

In this study we evaluated an implant that combines the advantages of a titanium tapered stem with a proximal anatomic geometry providing near-custom fit and fill of the proximal femur, which is the design feature that we believe allows immediate full weight bearing.4,28,29 The patients included in this study had a broad range of ages, diagnoses, and Charnley and Dorr classifications. The results demonstrate such an implant can provide excellent outcomes with regard to clinical and radiographic evaluation, and specifically, reliable osseointegration without risk of subsidence can be obtained with this implant despite immediate full postoperative weight bearing in patients with Dorr A and B proximal femoral-bone morphology.

The arthroplasty literature is replete with reports supporting an initial period of protected weight bearing after cementless femoral stem implantation. Although there seems to be a trend for surgeons to allow increased weight bearing immediately postoperatively, this practice has yet to be validated scientifically. This study is the first to establish that stable osseointegration without subsidence can be accomplished when immediate full weight bearing is permitted.

The patients in this large series were allowed immediate unlimited postoperative weight bearing, and 99.5% of femoral stems osseointegrated reliably. Two instances of aseptic loosening occurred, both in patients with abnormal proximal femoral anatomy as a result of previous surgery. There was a statistically significant increased risk of subsidence for patients with Dorr C bone. Therefore, we recommend this prosthesis not be implanted in patients with Dorr C bone or in patients with abnormal proximal femoral anatomy. Our findings indicate this stem will osseointegrate reliably without subsidence in patients with Dorr A or B bone despite immediate full weight bearing postoperatively.

References

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Authors

Dr Taunt is from the Michigan Orthopedic Center, Lansing, Michigan; Dr Finn is from the University of Chicago, Chicago, Illinois; and Dr Baumann is from Doctor’s Hospital, Columbus, Ohio.

Dr Taunt has no relevant financial relationships to disclose, and Drs Finn and Baumann are consultants to Biomet Inc.

Correspondence should be addressed to: Charles Taunt Jr, DO, Michigan Orthopedic Center, 2815 S Pennsylvania Ave, Ste 204, Lansing, MI 48910.

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