With the increasing interest in less invasive surgery, the unicompartmental knee arthroplasty (UKA) is experiencing a resurgence in popularity.7,12,33,48 Although many less-invasive procedures remain in the early stages of investigation, UKA has been part of the armamentarium for treatment of localized arthritis for 30 years.15,42,44 The ideal patient traditionally is thought to be elderly (60-70 years) and sedentary.8,10,15,46 With the elderly population increasing and living longer,28 the reliability and durability of UKA remain to be investigated, specifically in the octogenarian population.26,35
Surgical treatment of knee arthritis in elderly patients is tolerated and beneficial.9,11,36 Octogenarians (> 80 years) with degenerative disease of the knee traditionally have been treated with total knee arthroplasties (TKA).4,22,27,51 Although octogenarians benefit from this gold standard procedure, there is morbidity and mortality are associated with performing TKAs in elderly patients. In contrast, some have suggested that appropriately selected patients undergoing UKA have lower morbidity, faster recovery, and a more physiologic return to function than with TKA.10,34,42,50 Whether these potential advantages hold true in octogenarians has yet to be established.
We evaluated whether UKAs in octogenarians were durable enough to last most patients the rest of their lives. We assessed the reliability of the procedure by whether the patients tolerated the surgery, improved clinically, survived long enough to benefit from the surgery, and were satisfied with the outcome.
MATERIALS AND METHODS
From 1978 to 1990, we performed 450 UKAs at our institution. We identified 28 consecutive patients (38 knees) who fulfilled the criteria of age of 80 years or older at the time of surgery, with a minimum 2-year clinical followup. During the same time, 500 TKAs were performed in octogenarians, indicating that approximately 7.5% of octogenarians were thought to be appropriate candidates for unicompartmental surgery. The average age of the patients was 82 years (range, 80-87 years). No selection or exclusion criteria were based specifically on patient comorbidities.
Inclusion criteria for UKA included symptoms and signs referable to the involved compartment, minimal patellofemoral symptoms, less than 5° to 10° flexion deformity, a flexion arc of at least 90°, a low activity level, no inflammatory arthropathy, an intact anterior cruciate ligament, and no more than mild fixed varus deformity.15,25,26 Patients not meeting these criteria were treated with TKAs. Twenty-three prostheses were implanted in 18 women and 15 prostheses in 10 men. The average height of the patients was 1.6 m (range, 1.5-1.9 m), and the average weight was 71 kg (range, 55-93 kg). Unicompartmental knee arthroplasties were performed in 13 left knees and 25 right knees. Thirty-one unicompartmental prostheses were placed on the medial side and seven were implanted on the lateral side.
We used the Robert Brigham unicondylar knee replacement (Johnson and Johnson Orthopaedics, Raynham, MA), a low-congruence cemented prosthesis with a titanium-backed tibial component.
We used a joint registry to identify the octogenarian study group. All data were collected by retrospectively reviewing hospital records. Operative notes and hospital course were examined thoroughly for any complications. Clinical visits, readmissions, and correspondences also were examined. The patients' height, weight, site of surgery, compartment of knee arthroplasty, and contact information were obtained from the medical records. Additional information including date of death and additional contact information of living relatives was obtained from the Social Security Death Index available on the Internet. The closest living relative was interviewed by telephone regarding UKA complications, revisions, and patient satisfaction. Knee Society knee and function scores were calculated from data collected from the joint registry and clinical visits.
We performed a Kaplan-Meier survivorship analysis for the study group comparing prosthesis survival (defined by an end point of revision surgery) with patient lifespan. Ninety-five percent confidence intervals were calculated and included with the survival curve. We performed log-rank tests to determine differences between the survival curves.
All patients were accounted for at the conclusion of the study as living or dead. Fifteen years after the index procedure, three of 28 (11%) patients remained living. One patient (95 years) has well-functioning bilateral UKAs 15 years postoperatively (Fig 1). The second living patient (98 years) has bilateral UKAs surviving 17 years postoperatively. The third living patient required revision surgery 10 years after the index procedure and is discussed below. The twenty-five deceased patients (33 knees) died at an average age of 94 years (range, 88-103 years). Comparison of Kaplan-Meier survivorship analysis of patient lifespan versus prosthesis revision showed a difference in survival with the prosthesis surviving longer than the patient (Fig 2). Log-rank testing revealed a difference (p < 0.0001) between survival rates with the prosthesis surviving longer than the patient (95% confidence interval [CI], 3.462-13.47).
The study group had a considerable lifespan beyond the index procedure, and the surgery was tolerated without complications. The average survival according to hospital records of the 38 knees based on patient death or prosthetic revision was 11.9 years (range, 5-19 years). Categorization of comorbidities before surgery was determined by the anesthesia medical record according to the American Society of Anesthesiologists physical status classification system. Fifteen patients were Class II (mild systemic disease) and 13 patients were Class III (severe systemic disease). No patients were categorized as Class I (normal healthy patient) or Class IV (severe systemic disease which is a constant threat to life). There were no intraoperative complications, major immediate postoperative complications (eg, arrhythmia, myocardial infarction, pneumonia, deep vein thrombosis, pulmonary embolus), or perioperative deaths. The three postoperative complications included one case of conjunctivitis and two urinary tract infections, all of which resolved uneventfully with medical management.
Only two knees of 38 (5%) subsequently required surgical intervention for failed UKAs. One patient had UKA converted to a TKA for catastrophic wear and the other patient had arthroscopic removal of a loose fragment of the femoral component. Living relatives were found and contacted regarding 30 (79%) of the 38 replacements. These relatives were the closest living relative and/or primary caregiver. They provided verbal confirmation of any surgical complications and conveyed patient satisfaction. Relatives for seven of the patients (eight of the studied unicompartmental replacements) were not able to be located (21%). However, medical records and correspondence with the seven patients revealed no evidence of complications or need for additional surgery. The average clinical followup for this patient subgroup was 5.6 years (range, 4-8.8 years). Additionally, there were no complications or surgical interventions at the latest followup. All seven patients were confirmed to be deceased by medical record or Internet search. These patients lived an average of 6 years (range, 1-15 years) after their last documented clinical visit. Of the two failures, the first occurred 5 years after the index procedure. The patient had swelling, discomfort, and a squeaking sensation in the affected knee before revision. Radiographs revealed complete loss of the joint space with an increased varus deformity. Aspiration of the knee revealed cloudy, gray-black fluid with multiple small black inclusions. These finding were consistent with catastrophic polyethylene wear that was confirmed at surgery. The prosthesis was revised to a Kinemax Plus® (Stryker Howmedica Osteonics, Allendale, NJ) primary total knee replacement system. The patient had no pain and had excellent function for the subsequent 11 years. He walked until the week before his death. The second failure occurred 10 years after the index procedure. The patient was reported as doing quite well until a fall onto his affected knee. The patient had increasing swelling and occasional discomfort. Radiographs revealed a fracture of the femoral component. The patient refused revision surgery and instead had knee arthroscopy for débridement and removal of the loose body (Fig. 3). Because arthroscopic removal proved too difficult, a 6-cm capsulotomy was made to remove the loose portion of the femoral component. The fragment was approximately 5 mm × 10 mm and the patient had mild improvement in his symptoms. At the latest followup 5 years after arthroscopy, the patient has yet to have additional surgery.
The reliability of UKA in these octogenarians was demonstrated by clinical improvements and satisfaction with outcome. At an average followup of 4 years (range, 2-9 years), Knee Society knee and function scores improved preoperatively from 46 and 45, respectively, to 85 and 71 postoperatively. Living family members reported the patients' expectations were completely met in 59%, mostly met in 31%, and partially met in 10%. When asked if the patient would have UKA if given the choice again, 69% were definite, 21% were most likely, and 10% were probable. Patients' overall satisfaction with the procedure was excellent in 84%, good in 13%, and fair in 3%. No family members reported poor results or “not at all” to any of the questions. Even the two patients who required revision surgery were thought to have benefited from several years of improved pain and function.
Recently, the success of UKA has become more prominent.8,47 Investigation of the reliability and durability of UKAs in the octogenarian population can determine whether it can out-survive the patient, and therefore be a viable alternative to a TKA. Surgery should continue to be considered a reasonable option in octogenarians because, as illustrated by our study group, they are expected to live, on average, an additional 8 to 10 years postoperatively.22,28 Octogenarians generally have more comorbidities and are at greater risk during surgery than the general population.17,26 For these reasons, less-invasive surgery that can offer reliable outcomes and durable results with fewer surgical and postoperative risks may be of value. Although the TKA is the gold standard treatment of arthritis in the elderly, UKA is a viable alternative in properly selected octogenarians.
A limitation of our study was the small study group available for review. Patients appropriate for unicompart- mental surgery in this age group comprise approximately 7.5% of octogenarians having TKAs. These surgeries also were performed by one surgeon (RDS) experienced in unicompartmental knee surgery. Using revision as an end point for survival has potential limitations because patients either may refuse or not be candidates for revision surgery secondary to health risks. However, other surgical treatments in this age group would be subject to the same limitation. In addition, patient satisfaction revealed that UKA met their expected goals. Although extensive medical record investigation found only two of 38 UKAs failed, family members of seven patients (eight knees) were unable to be contacted. However, King et al reviewed patients who had 200 TKAs with 17% not returning for followup at an average of 5 years, but they reported no significant differences in knee pain, function, or revision from patients who were not lost to followup.24 Patients who did not achieve complete followup were not assumed to have worse outcomes than patients with complete followup.24 Furthermore, the clinical followup of the seven patients averaged 5.6 years and there was no evidence of complications or need for revision.
There are few studies that specifically examine knee arthroplasties in the elderly. Total knee arthroplasty is the gold standard procedure in the octogenarian population based on the assumption that it may obviate the need for additional surgery.4,22,27,51 In general, total joint arthroplasty in the elderly has been shown to be beneficial and safe.6,9,11,36,37 However, this procedure is not without potential complications.41 Kreder et al reported that octogenarians having hip or knee arthroplasty were 3.4 times more likely to die, and three times more likely to experience substantial perioperative complications compared with patients younger than 80 years.23 Increasing patient age is a risk factor for mortality after a primary TKA.17,40 The risk ratio of mortality in patients 85 years or older was 14 times greater than for younger patients.17 Specific to the TKA in the elderly, the majority of studies show a perioperative mortality rate of 2% to 3%.1,6,21,51 In the minority of studies that do not show similar mortality rates, medical complications are frequent with rates as much as 40% to 50%.5,26,37 In addition, survival of TKAs in octogenarians is reported with revision rates ranging from 3% to 5% with only 1.5 to 4.5 years followup.2,13,20-22,27 With short-term followup, the revision rate is reported to be as much as five times greater than TKAs in the general population.14
As an alternative to the TKA, UKA has been described to have certain perioperative advantages and improved outcome in the properly selected patient.10,34,42,50 In a prospective study, Newman et al randomized more than 100 knees suitable for unicompartmental surgery to UKA or TKA groups.34 The UKA group had less perioperative morbidity, less blood loss, recovered more quickly, regained motion more rapidly, and had shorter hospital courses. Other studies suggest UKA is a less invasive procedure with perioperative advantages.10,42,50 Although our study group was small, there were no perioperative deaths or substantial perioperative complications in the 38 UKAs performed. These potential benefits may be valuable to the octogenarian population burdened with more comorbidities. This potential advantage of less perioperative morbidity compared with TKAs would be best addressed in future prospective studies.
Even if UKA posed less risk to octogenarians, it would need to provide equal clinical improvements to be considered a viable alternative. Octogenarians objectively benefited from UKAs as measured by knee scores, and subjectively as reflected by patient satisfaction. Short-term followup revealed improvement in Knee Society knee and function scores similar to scores after TKAs in octogenarians.21,22,27 Excellent and good results for knee and function scores were obtained in 83% and 70% of patients, respectively. Although it is difficult to continue uniform clinical followup until patient death, relatives reported 90% patient satisfaction in meeting expectations and a desire to have the surgery again.
Long-term success of UKAs in properly selected patients has been well-documented.3,29,47,49 Berger et al reported a 98% 10-year survival rate using radiographic loosening or revision as an end point.8 In a 10-year followup of UKAs by Heck et al, survivorship was reported to be 91%.19 With this type of durability, the question arises whether UKA is sufficiently durable that it can out- survive the octogenarian to serve as a definitive treatment for knee arthritis.
In this study, a survival analysis of the prosthesis versus the patient revealed that the majority of the octogenarians were outlived by UKA (Fig. 2). In all but two of 38 knees (5%), patient death occurred before revision knee surgery. Unicompartmental knee arthroplasty was durable and sufficient to serve as the definitive procedure. The lower stresses placed on the prosthesis by the elderly patient may partly explain the length of prosthesis survival. The most common causes of UKA failure are component loosening and polyethylene wear.14,29 Although four patients had 6-mm composite inserts, none had complications or required revision surgery. This threshold is notable because failures have been attributed to inadequate polyethylene thickness.16,30-32,38,45 Progression of arthritis in the uninvolved compartment is also a major cause of UKA revision.18 None of these complications was the cause of revisions in our study. The two knees requiring surgical intervention at an average of 7.5 years after implantation were catastrophic type failures. Complete failure of the polyethylene spacer with metal-on-metal articulation is rare with modern implants and techniques.38,43 This type of failure is similar to that reported for polyethylene sterilized in air.31,38 In addition, femoral prosthesis fracture is indicative of a manufacturing malfunction more so than a traditional mechanism of failure. This type of failure was documented in a previous case report.39 With both failures secondary to design flaws, it seems possible that current implant technology and technique may further minimize the occurrence of these rare failures. Although the octogenarians survived nearly 12 years postoperatively, all but two patients were outlived by their prostheses. Therefore, UKA seems to be a durable and viable option to a TKA as a definitive treatment of arthritis for octogenarians.
Knee arthroplasty should be considered a reasonable treatment for arthritis in octogenarians, as they are expected to live an additional 10 years postoperatively.28 Although the TKA remains the standard treatment for octogenarians with arthritis, UKA should be considered a viable alternative in the properly selected patient. At our institution, approximately 7.5% of octogenarians having TKAs were suitable candidates for UKAs. Elderly patients subjected to same selection criteria for UKAs as the general population tolerated the procedure with minimal complications, achieved short-term clinical improvements, were satisfied with the results and, except for two patients, died before the prosthesis failed. Future studies are needed to define the precise role of UKA in octogenarians.
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