Background/Introduction

As a new generation of robotic systems is introduced into the world of arthroplasty, Robotic-Assisted Total Knee Arthroplasty (TKA) represents a growing proportion of a reconstructive surgeon's operative volume. This study aims to compare the post-operative readmission rate, pain scores, costs, as well as the effects on surgeon efficiency one year after adoption of these technologies into clinical practice.

Introduction: Osteolysis of the pelvis secondary to polyethylene wear of uncemented acetabular implants has emerged as the most serious and challenging consequence of THR. A very large number of patients have and will continue to receive implants at the risk of being associated with osteolysis. The early detection of osteolysis allows the initiation of treatment programs that preserve bone stock. Because osteolysis occurs and progresses in the absence of clinical symptoms, appropriate follow-up surveillance must be instituted. Our initial study of the usefulness of CT scans in detecting clinically silent and radiographically unobservable osteolysis indicated that x-rays greatly understated the incidence and location of osteolysis. The purpose of this study was to determine the incidence of CT scan identifiable osteolysis in young, active patients with a single cup design and a minimum follow-up of 7 years.

Methods: Between 1990–1995, 117 hips (105 patients) underwent an uncemented total hip replacement with a patient-matched femoral component and a titanium plasma sprayed, multi-holed acetabular shell with a compression molded, polyethylene, irradiated in air. 57 patients underwent a CT scan using a metal subtraction software technique. All patients were classified based on their CT scans: Group I: no osteolysis; Group II: cavitary osteolysis; Group III: segmental osteolysis. All patients had standard AP, Frog – lateral and shoot-through lateral radiographs, performed at the time the CT scan was obtained.

Results: 37.2% of hips were in Group I, 53.5% in Group II and 9.3% in Group III. No patients in Group I had x-ray evidence of osteolysis (i.e. there were no false negative CT scans). 12% of patients in Group II had x-ray evidence of osteolysis. 22% of patients in Group III had x-ray evidence of osteolysis. There was no correlation between the incidence of osteolysis seen on CT scans with: 1) activity level; 2) age; 3) sex; 4) weight, and 5) size of acetabular component. There was no correlation between polyethylene wear measured using the Martel method and pelvic osteolysis. There was a correlation between the length of implantation and pelvic osteolysis. The average follow-up for patients in Group III was 105.5 months (range 85 – 115) vs. 89.4 months (57 – 117) for Group II and 81.5 months (51 – 112) for Group I. Of the patients with follow-up greater than eight years, 25% had Group III osteolysis. No patients have required revision or polyethylene liner exchange thus far.

Discussion: This study indicates that: 1) x-rays are an unreliable method for determining the presence. Location or extent of osteolysis, 2) the incidence of osteolysis based upon CT scans (Group II – III) is 63%; 3) Osteolysis, even if extensive (Group 3) is NOT associated with symptoms; 4) the pattern of osteolysis seen on CT scan strongly suggests that the presence of screws plays an important factor in the process; 5) CT scans are helpful in the planning process for acetabular revision. They allow the precise determination of the location and extent of osteolysis; 6) CT scans are also potentially useful for determining the impact of medical (e.g. alidronate) or surgical (e.g. bone grafting) treatment of osteolysis; 7) CT scans may be very helpful in assessing whether new polyethylenes are associated with reduced osteolysis.

The authors strongly recommend that: 1) a surveillance program be established for careful, regular follow-up of patients with THR in place more than 7 years; 2) CT scans be considered as part of that surveillance program, and 3) cups with screws NOT be used routinely in primary THR surgery.

Pelvic osteolysis secondary to polyethylene wear is a major complication following THR. Identification of implant specific characteristics associated with osteolysis is essential. The purpose of this study is to compare incidence of CT scan identifiable osteolysis in 2 groups of young, active patients following THR; one with multi-holed acetabular shells with screws, one with cups without screw holes.

Between 1990–1993, 77 patients (85 hips) underwent THR with a cementless titanium, multi-holed shell with screws, modular, compression molded polyethylene and an uncemented titanium femoral stem. Average follow-up: 9 years, average age at surgery: 51 years. Between 1984–1987, 163 patients (183 hips) underwent THR with a cementless cobalt-chrome, solid shell, modular, heat-pressed polyeth-ylene liner and uncemented cobalt-chrome femoral stem. Average follow-up: 16 years, average age at operation: 52 years. All polyethylene was irradiated in air. At most recent follow-up, CT scans with metal suppression software was obtained to evaluate incidence of pelvic osteolysis. Patients classified: Group 1-no osteolysis, Group 2-cavitary osteolysis, Group 3-segmental osteolysis.

Patients with titanium, multi-holed shells had: Group 1-50.0%, Group 2-38.7%, and Group 3-11.3%. Patients with cobalt-chrome, solid shells had: Group 1-59.3%, Group 2-33.3% and Group 3-7.4%.

Although the patients with solid cups had much longer follow-up, less secure capture mechanism, less congruency between polyethylene and shell, and heat-pressed polyethylene, the incidence and extent of pelvic osteolysis was less than in the patients with multi-holed shell with screws. The presence of 6.5 mm cancellous screws is a serious independent risk factor for pelvic osteolysis following THR.

Since acetabular osteolytic lesions following total hip arthroplasty (THA) may be asymptomatic until extensive bone loss occurs, early detection and monitoring the progression of these lesions is important. The purpose of this study was to use high resolution helical CT to determine the progression of the osteolytic lesions over time by comparing serial studies.

Fifty patients (Fifty-eight hips) with primary, cementless THA done between 1984–1996 were evaluated as part of an ongoing prospective study. These patients had a history of a high level of activity that was believed to place them at increased risk for accelerated polyethylene wear. The mean age was 51 yrs, 55% male:45% female. The average time from date of surgery to initial scan was 8.0 years (4.7–16.6). If an acetabular lytic lesion was identified, the patients were offered Alendronate for potential suppression of bone resorption with a repeat CT scan for follow-up. The area of the maximum size osteolytic lesions on axial images were measured on the initial scan and compared at the same level on the subsequent study.

The interval between scans averaged 15 months (10 – 27). Progression was noted on 87% hips. The mean initial area was 328 mm2 (40–1084) with the follow-up area of 386 mm2 (46–1344) with a mean of progression of 15.7%.

Once established, peri-acetabular lysis appears to be a slowly progressive, relentless process. Analysis of changes on serial CT, along with an assessment of the degree and location of lysis, provides an additional tool to evaluate the need for surgical intervention.