Unicompartmental Knee Arthroplasty for More than One Compartment
Preoperative radiographs of the left knee including (a) standing AP, (b) standing flexion 45-degree PA, (c) lateral and (d) sunrise views. These radiographs demonstrate degenerative changes including medial compartment joint space narrowing, sclerosis, and osteophyte formation with an associated varus alignment and only moderate joint space narrowing of the patellofemoral compartment
Options were discussed with the patient, including conservative management, medial unicompartmental, and total knee arthroplasty. The patient elected to proceed with medial unicompartmental knee arthroplasty , and this was performed without complication. At the time of surgery, it was noted that there was a small 4 mm area of grade 4 change on the lateral trochlea of the patella, but the remainder of the patellofemoral and the lateral tibiofemoral compartments were completely normal. The implant used was a Biomet Oxford mobile-bearing unicompartmental knee , and postoperative radiographs showed appropriate component positioning with restoration of neutral joint alignment (Fig. 11.2a–c).
The patient did very well for 5 years, at which time he presented to clinic with worsening knee pain anteriorly in the patellofemoral compartment. He had no history of trauma or infection but complained of throbbing pain worse after sitting or standing for prolonged time, particularly under the knee cap. On examination, the patient had well-healed incision with no erythema or evidence of infection, active range of motion from 0 to 120 degrees, and stable to varus and valgus stress. He had maintained strength 5/5 in flexion and extension, with painless hip range of motion. All infectious markers were negative. We routinely draw an erythrocyte sedimentation rate (ESR) and a C-reactive protein (CRP) initially. We also perform an aspiration to assess cell count with differential stain, Gram stain, and cultures. Radiographs demonstrated well-fixed medial unicompartmental arthroplasty components, with no evidence of loosening with maintained component alignment. There was evidence of progressive degenerative changes in the patellofemoral compartment , with significant joint space narrowing (Fig. 11.3a–d). He was prescribed a period of activity modification, therapy, and prescription of NSAIDs without relief. Additionally, a corticosteroid injection was performed, which improved symptoms only temporarily.
Ultimately, the patient was offered the option of isolated patellofemoral arthroplasty versus revision of medial unicompartmental knee arthroplasty to total knee arthroplasty. We explained that at the time of surgery, we would perform a thorough evaluation of the existing components in the medial compartment as well as the cartilage in the patellofemoral and lateral compartments . In the event that there were both lateral compartment and patellofemoral compartment degenerative changes, we would perform a conversion to a total knee arthroplasty. If the lateral compartment was spared, we were prepared to perform an isolated patellofemoral arthroplasty. After explaining all of the risks and benefits to the patient, he elected to proceed with patellofemoral arthroplasty.
An anteromedial incision was made using the previous surgical incision and a medial parapatellar approach utilized. Inspection of the joint at the time of surgery revealed severe degeneration of the patellofemoral joint with exposed bone-on-bone changes, present on both the patellar and trochlear side (Fig. 11.4a, b). The medial Oxford components were well fixed and well maintained with no signs of loosening (Fig. 11.4c). The polyethylene was well maintained with no signs of wear. The polyethylene was removed, and a thorough lavage was carried out. A new polyethylene was inserted. The previous size was 4 mm, and after assessing balance throughout the arch of motion, a 4 mm polyethylene was used. Inspection of the lateral compartment revealed intact surfaces with no defects or significant changes. The meniscus was intact laterally, as were the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) . As such, it was determined to proceed with isolated patellofemoral arthroplasty using a Zimmer patellofemoral component .
We began with preparation of the patella. The patella was displaced laterally and the femoral canal entered. Using an intramedullary guide, the appropriate rotation was verified with the transepicondylar axis and the anterior cut was made. The femur was sized for a #4 femoral component with excellent coverage and no overhang. The femur was then prepared using the milling system with drill holes for peg fixation (Fig. 11.4d, e). Trial reduction was performed, and there was excellent tracking of the patellofemoral joint with no impingement and normal tracking with no lateral release required. The final implants were cemented in place using antibiotic cement (Fig. 11.4f). The wound was irrigated and closed with a layered closure.
Postoperative radiographs demonstrate medial unicompartmental knee arthroplasty with patellofemoral knee arthroplasty (Fig. 11.5a–c). The patient did well in the immediate postoperative period with improvement in pain and function but did develop some laterally based pain concerning for soft tissue (lateral retinaculum) scarring over the lateral aspect of the patellofemoral implant consistent with impingement. He ultimately underwent an arthroscopic procedure, which revealed extensive scarring and adhesions with fibrotic bands over the superolateral area. These were removed arthroscopically, and further assessment of the joint demonstrated well-fixed components, no excessive wear of the medial polyethylene, or patellar polyethylene. Excellent alignment and tracking were demonstrated intraoperatively as well as maintained lateral cartilage, meniscus, and ligaments. The patient improved after this procedure, and we are continuing to follow his progress.
The majority of the recent literature regarding bicompartmental knee replacement focuses on the combination of patellofemoral and unicondylar arthroplasty , with medial compartment arthroplasty being more common than lateral [19, 20, 23–29]. Of the nine studies and 255 cases included here, approximately seven-eighths involved medial compartment arthroplasty and two-thirds of patients were female (Table 11.1). At a mean follow-up of 3.4 years, only seven of 255 (2.7%) of the bicompartmental arthroplasties had been revised to TKA, and no UKAs were revised to another UKA. Complications requiring reoperation but not revision included a lateral retinacular release for patellar subluxation , two subsequent UKAs (one lateral and one medial) in the remaining compartment for progression of arthritis , two manipulations under anesthesia for arthrofibrosis, and one subsequent patellar resurfacing . It is worth noting that both of the manipulations, and the one subsequent patellar resurfacing, occurred in patients who did not have the patellar resurfaced at the time of the index procedure , which is atypical for the included cases. Three of these seven revisions were secondary to aseptic loosening of the tibial component [26–28]. One revision was performed for each of the following indications: tibiofemoral instability , traumatic fracture during an MVA , progression of the remaining compartment, and deep infection treated with two-stage exchange . An additional two patients had degeneration of the remaining compartment (one lateral and one medial) treated with a subsequent unicondylar arthroplasty and resolution of symptoms . Those authors did not consider this to be a revision or treatment failure, as the index components remained well fixed , and staged bicondylar knee arthroplasty has also been reported for the treatment of disease progression after medial UKA . The proponents of bicompartmental arthroplasty would argue that this highlights an advantage of both unicompartmental and bicompartmental arthroplasty. Namely, replacing each arthritic compartment with a discrete unicompartmental prosthesis allows for subsequent unicompartmental replacement in the case of arthritic progression of a remaining native articulation despite appropriate functioning of the unicompartmental arthroplasty [19, 28]. This unicompartmental to bicompartmental “conversion” procedure has been described in as being successful in the variety of the possible iterations: an index unicondylar arthroplasty with later addition of a PFA , an index PFA with later unicondylar arthroplasty , and an index medial unicondylar arthroplasty with subsequent lateral unicondylar arthroplasty . However, the numbers of such cases are quite limited and there is not sufficient evidence for any meaningful inferential meta-analysis.
Patellofemoral arthroplasty + medial or lateral unicompartmental arthroplasty