All surgery was performed by the senior authors (JMA, JNA). In the bi-UKA group, the surgical approach was a standard medial parapatellar approach for 70 knees (70%) and a standard subvastus approach in the remaining 30 cases (30%). In the med-UKA/PFA group, the surgical approach was a standard medial parapatellar approach for 42 knees (55%). A subvastus approach was performed in the 35 knees (45%) with a history of patellar dislocation or trochlear dysplasia to manage the external retinaculum release without compromising the patellar blood supply. All UKA components were cemented on the tibial and the femoral side. Between 1972 and 1989, Zimmer Condylar 2 (Zimmer, Warsaw, IN) or Alpina (Biomet, Bridgend, UK) were used as UKA implants either in the medial or the lateral compartment. After 1989, Miller-Galante UKA (Zimmer) were systematically used and performed with modern dedicated instrumentation, including tibial and femoral cutting guides. In the med-UKA/PFA group, all patients had an autocentric patellofemoral prosthesis (DePuy, Warsaw, IN) with a cemented polyethylene (PE) patella and a Co-Cr femoral component cemented in 40% of the cases. The design characteristics and the surgical technique of this device have been previously described [4, 5] (Fig. 1).
Postoperative rehabilitation protocols included immediate weightbearing protected by crutches during the first 2 or 3 weeks according to patient tolerance, and exercises were focused on passive flexion immediately and then active recuperation of flexion and extension. All patients received routine prophylaxis with fractionated heparin in the 1970s and 1980s and later this protocol was changed to low-molecular-weight heparin pre- and postoperatively for 21 days.
All patients were evaluated clinically preoperatively, at 3 months postoperatively, at yearly intervals postoperatively, and at last followup by one observer (SA) not involved in the treatment using the Knee Society knee and function score . For the patients operated on in the 1970s and 1980s, the data collected on the standardized knee sheet used in the department during this period were used to calculate the Knee Society score . We recorded the arc of knee flexion preoperatively, during followup, and at the final evaluation.
Radiographic evaluation was performed by one observer (SP) on long-leg radiographs and on anteroposterior (AP), lateral, and skyline radiographs of the knee obtained postoperatively and at last followup. The lower-limb alignment was assessed on long-leg radiographs performed using a standardized protocol in which the patient stood with the patella facing anteriorly. On these long-leg radiographs, pre- and postoperatively, the femoral angle (CH: condylar axis to hip center), the tibial angle (PA: plateau axis to ankle), and the articular deformation (CP: condylar axis and plateau axis) were calculated [11, 12]. Then the hip-knee-ankle (HKA) angle was calculated as the sum of the three previously defined angles (HKA = CH + PA + CP) considering CP as positive in case of lateral convergence [11, 12]. We assessed postoperative alignment of the femoral and tibial components as well as the postoperative alignment of the limb on long-leg radiographs with the same standardized protocol used preoperatively [11, 12] (Fig. 2). We examined full tangential AP and lateral radiographs and skyline radiographs to detect the presence, extent, and progression of femoral, tibial, or patellar radiolucencies; we considered lucencies greater than 1 mm, irregular, or progressive between two radiographic examinations as relevant according to the Knee Society roentgenographic score . The restoration of the mechanical axis was also analyzed postoperatively and at final followup according to the Kennedy classification, which considers the alignment correct when the mechanical axis is in Zone 2 or C (central) . This classification divides the knee into fives zone: Zone 0 is medial to the medial part of tibial plateau, Zone 1 is the medial half of the medial plateau, Zone 2 is the lateral-half of the tibial plateau, Zone C is the area of the tibial spines, and Zone 3 is the medial part of the lateral plateau . Furthermore, progression of OA was evaluated in the nonresurfaced compartment on AP radiographs and in the patellofemoral joint on skyline radiographs . The Ahlback classification was used to evaluate OA progression in the medial or femoropatellar compartment .
Patient demographics were described using means and standard deviations or medians and ranges for continuous variables and counts (percent) for categorical variables. A descriptive report of the radiographic outcomes was performed using means and standard deviations to describe pre- and postoperative alignment. Survival analysis was performed using the Kaplan-Meier technique (with 95% confidence intervals) for all patients considering revision for any reason or radiographic loosening as the end point . Analysis was performed using SPSS software (Version 12; SPSS Inc, Chicago, IL). All calculations assumed two-tailed tests.
Bicompartmental arthroplasty reliably alleviated pain and improved the Knee Society knee and function scores, respectively, improved from 44 ± 6 (range, 25-64) to 88 ± 2 (range, 65-100) and from 38 ± 8 (range, 14-65) to 84 ± 10 (range, 59-100) in the bi-UKA group and in the med-UKA/PFA group; and from 42 ± 8 (range, 17-59) to 88 ± 2 (range, 58-100) and from 35 ± 9 (range, 10-57) to 79 ± 15 (range, 58-100). In the bi-UKA group, the mean active knee flexion improved from 112° ± 5° (range, 100°-145°) preoperatively to 136° ± 4° (range, 117°-149°) at final followup. In the med-UKA/PFA group, the mean active knee flexion improved from 118° ± 9° (range, 100°-150°) preoperatively to 134° ± 6° (range, 120°-153°) at final followup.
Bicompartmental arthroplasty demonstrated mixed results in regard to durability with a 17-year survival to revision, radiographic loosening, or disease progression of 78% (95% confidence interval, 0.73-0.83) in the bi-UKA group and 54% (95% confidence interval, 0.47-0.61) in the med-UKA/PFA group (Fig. 3A-B). Twenty-five knees (15.5%) showed radiolucencies (less than 1 mm) at the tibial bone-cement interface without any sign of progression after 5 years of followup. No femoral radiolucencies were observed.
The mechanical axis of the lower limb was correct and stable at last followup (Table 3). At last followup, the mean AP axis of the tibial component was 89° ± 3° (range, 85°-90°) on the medial side and 90° ± 2° (range, 88°-93°) on the lateral side. Mean tibial slope was 3° ± 4° (range, 0°-8°). The mean AP femoral axis was 92° ± 7° (range, 86°-94°).
At last followup, 14 knees were asymptomatic (without any change in the clinical score) OA progression in the patellofemoral compartment in the bi-UKA group and six knees presented isolated asymptomatic OA progression in the lateral compartment in the med-UKA/PFA group.
In four cases in the bi-UKA group, avulsion of the anterior tibial spine was observed intraoperatively, requiring intraoperative fixation using nonabsorbable suture without adverse effects on the final outcome. No other intraoperative complications were observed. Twelve patients had postoperative deep venous thromboses and were treated with a therapeutic dose of fractioned heparin in the 1970s and 1980s and with low-molecular-weight heparin later. In the bi-UKA group, 17 knees underwent a revision at a mean of 6.5 years (range, 9 months to 12 years), 16 for aseptic loosening and one for a symptomatic progression of OA in the patellofemoral compartment. Among the 16 aseptic loosening cases, eight involved loosening of both the medial and lateral implant, five of the medial implant and three of the lateral one. The failures were related to polyethylene wear and loosening of the tibial plateau for all the cases in the lateral and in the medial sides. Most of the revised patients (13 of 16) were operated on before 1989. Ten knees were revised using a conventional posterostabilized TKA with a tibial stem and eight knees with a hinged prosthesis. One knee was revised for progression of OA in the patellofemoral compartment at 10 years by addition of a patellofemoral implant with a good result at final followup of 15 years. In the med-UKA/PFA group, 28 knees underwent revision, 27 for aseptic loosening at a mean of 7.9 years (range, 11 months to 22 years) and one knee for septic loosening at 4 months. Among the 27 aseptic loosening cases, 20 knees had an isolated loosening of the patellofemoral implant and seven knees had loosening of the medial UKA related to PE wear and loosening of the tibial plateau. Among the 20 loosening of the patellofemoral implant, 15 were uncemented PFA performed before 1989 and five were cemented. Revisions were performed using a conventional posterostabilized TKA with tibial stem and augments when required (Fig. 4A-D). The knee with septic loosening required a two-stage revision.
Bicompartmental arthroplasty has been advocated as an alternative to TKA for limited arthritis of the knee to preserve bone stock and restore more normal kinematics [14, 16-18]. As a result of these potential advantages over TKA, there is a renewed interest for combined compartmental implants, including combined medial UKA and femoropatellar arthroplasty and combined medial and lateral UKA [14, 16-18]. To confirm the durability of bicompartmental arthroplasty observed in the historical series , and considering short-term objective and subjective functional improvements recently reported after combined bicompartmental implants [16, 18, 30], we asked whether (1) bicompartmental arthroplasty (either combined medial UKA and femoropatellar arthroplasty or combined medial and lateral UKA) reliably improved Knee Society pain and function scores; (2) bicompartmental arthroplasty was durable (survivorship with the end points of revision, radiographic loosening, or symptomatic disease progression); and (3) we could achieve durable alignment; and (4) whether arthritis would progress in the unresurfaced compartment.
We note some limitations in our study design. First, we included different types of implants performed during a long time period with a major evolution in both the instrumentations and the implants over that time. These data include patients in whom we used relatively crude techniques and early-generation components no longer in use. Second, we did not match our patients with patients operated for a TKA during the study period to directly compare the results of TKA and those of bicompartmental arthroplasty. Third, we were also unable to perform a contemporary evaluation of the functional results including a subjective evaluation using a knee-related quality-of-life questionnaire (such as the Knee Osteoarthritis Outcomes Score) [28, 31] and an objective functional evaluation tool such as gait laboratory analysis or three-dimensional fluoroscopy because most of these methods of evaluation were not available at the time of the early operations [7, 16-18, 27]. Despite these limitations, we report a relatively homogenous and continuous series of patients operated on in the same department for either a combined medial and lateral UKA or a combined medial UKA and patellofemoral arthroplasty by the same two senior authors (JMA, JNA) using a cemented metal-backed implant for the UKA and the same patellofemoral implant.
One of the primary aims of bicompartmental arthroplasty is to restore more normal knee kinematics and function by preserving the bone and the ligaments of the patient [7, 10, 16-18, 30]. In fact, this bone and ligament-sparing technique can be considered minimally invasive surgery, not only for the skin and the muscular tissue, but also for the structures inside the knee [7, 10, 16-18, 30]. This is confirmed by our data observed in the series of bicompartmental arthroplasty reported in the literature (Table 4) [7, 10, 14, 17, 20, 34]. According to kinematic and gait studies, knees with biunicondylar arthroplasty can provide excellent functional outcomes in appropriately selected patients close to those observed with UKA. One study  suggests results are better for patients with preserved cruciate ligaments, and in our series, preserved cruciate ligaments was one of the most important criteria to confirm the indication of bicompartmental arthroplasty. Our data and that in the literature confirm that bicompartmental arthroplasties could be proposed as an alternative to TKA . To date, there are limited outcome data to our knowledge reporting the short-, mid-, or long-term outcomes of bicompartmental arthroplasty and no report of combined medial UKA with patellofemoral implant. The concept of a new monobloc bicompartmental implant combining a medial UKA and a patellofemoral implant has been recently described but there are no outcome data available yet [14, 30].
Survivorship to revision at 17 years was lower than observed for TKA or UKA in both groups. We observed a relatively high revision rate, particularly concerning the med-UKA/PFA group. This high revision rate may be related to early generations of implants. The results may be improved with enhanced instrumentation and techniques, better PE, and contemporary designs. Furthermore, at the beginning of the experience, no instrumentation was available for surgical guidance. In case of failure, bone stock was preserved and revision considered easier than a revision performed after TKA. In the med-UKA/PFA group, failure was related to the patellofemoral implant for 20 knees of 27 revised for aseptic loosening. Improvement in implant design and fixation may improve these results in the future, particularly concerning the patellofemoral joint. In our study, only one patient in the bi-UKA group underwent revision for symptomatic OA progression in the patellofemoral compartment. This relatively low rate of symptomatic OA progression is probably related to proper preoperative screening, particularly concerning the patellofemoral compartment. If careful clinical screening and stressed radiography remain the key points for patient selection, quantitative evaluation of the cartilage status using modern dedicated tools such as T2 mapping may be helpful in the future to optimize patient selection .
Due to renewed interest in bicompartmental arthroplasty, we report our mid- and long-term results of combined medial and lateral UKA and combined medial UKA and patellofemoral arthroplasty. Our data suggest this concept improves function and restores limb alignment restoration for moderate deformities. A relatively high revision rate was observed compared to TKA series and these failures may be related to early generation of implant and limited instrumentation. In contrast, we observed few cases of progressive OA confirming the indication for bicompartmental arthroplasty in case of bicompartmental arthritis of the knee. We believe partial knee replacement with less bone loss and the potential for greater function an important concept. The concept with new implants and appropriate instrumentation will require confirmation using contemporary objective tools to confirm its usefulness.
We thank Mrs Suzanne Aznavourian for clinical review of the patients.
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