While many studies describe MUKA, there are far fewer studies describing pain relief and restoration of function after LUKA [4
]. Even when the procedure is reported in the literature, the numbers in the studies are small and the surgical approach is either via a medial parapatellar, not described, or rarely described as being via the lateral parapatellar [36
]. We therefore examined our indications for LUKA, how we perform this procedure, and the subsequent Knee Society scores, ROM, and revision and reoperation rates.
There are a number of limitations to our study. First, we have specific indications for surgery and the findings might not apply to other indications. We cannot define the indications for LUKA from our study design. However, we found utilizing stress radiographs or arthroscopy yielded a low reoperation rate. We do not know how many patients might have been candidates for LUKA but had TKA performed based on poor stress radiographs or findings at diagnostic arthroscopy. Second, we were unable to contact 13 of the 125 patients (13 knees) for 2-year followup. While these patients had an average Knee Society total score of 92 and an average pain score of 44 at last followup, their revision status remains unknown. Third, given the fact that in nearly ½ of the patients we assessed the final outcome by telephone, we did not perform a radiographic analysis and cannot comment on progression of disease, component fixation, or component and limb alignment. Lastly, the followup in our series is short at only an average of 39 months. Therefore, we did not perform a survivorship analysis and simply reported the reoperation rate.
The rate of UKA is growing at a three times faster rate than TKA in younger patients [38
]. Therefore, it is important for surgeons to understand the indications for these procedures. Vince and Cryan [43
] postulated dependable survivorship and pain relief after UKA encourage surgeons to expand the indications for UKA to include younger and more active patients. Pennington et al. [36
] reported on LUKA in younger and more active patients with cemented, metal-backed or all-polyethylene tibial components and found a survivorship of 100% at an average followup of 12.4 years (Table ). Pennington et al. [35
] specifically reported on younger patients receiving UKA and noted 100% survivorship at an average followup of 11 years and 91% good/excellent results, which is similar to our results after LUKA via a lateral parapatellar approach. We determined candidacy for LUKA either by correction of deformity and maintenance of medial joint space on a varus stress radiograph or by prearthroplasty arthroscopy, but not based on age. With the low failure rate in our series, we cannot determine superiority between the radiographic and arthroscopic methods of confirming isolated disease. More arthroplasty-based surgeons may prefer to utilize the radiographic approach, while surgeons with more experience using arthroscopy may prefer that method. Regardless, justification of both methods via our results is an original finding of our study.
The large number of patients in this series also makes it relevant. An early study of UKA included 100 patients, 88 of whom had MUKA and only 12 of whom had LUKA [41
]. At an average followup of 3.5 years, three failures were noted: one MUKA and two LUKAs. Argenson et al. [4
] reported on a similar mixed cohort with small numbers where the study group included 15 LUKAs and a 10-year survival of 93%. One of the 15 LUKAs had revision to TKA due to patellofemoral osteoarthritis progression. Marmor [29
] examined the outcomes of LUKA in a cohort of 14 knees. That study used a cemented, all-polyethylene tibial component coupled with a cemented femoral component. At final followup, two patients underwent revision for a 7.4-year survivorship rate of 85%. Subsequent studies have reported 82% to 93% survival with the same implant design, yet the number of knees remained small in these series [9
]. In the series with perhaps the longest followup, O’Rourke et al. [33
] noted 72% survival in 14 LUKAs at 24 years. In recent studies with fixed-bearing, cemented tibial implants, Argenson et al. [7
] reported a prosthesis survivorship of 92% at 10 years and 84% at 16 years. Sah and Scott [39
] described LUKA through a median parapatellar arthrotomy in 49 patients and observed no revisions at 5.4 years postoperatively. However, it should be noted LUKA was abandoned in more than ½ of the cases via the medial parapatellar approach [39
]. By using preoperative varus stress radiographs or diagnostic arthroscopy before LUKA, there were no patients in our study for whom we intraoperatively made a decision to perform TKA, and we performed all surgeries through a less invasive lateral parapatellar approach. Our study, examining metal-backed tibial designs with an average 39-month followup, demonstrated only one revision (1%) using pathoanatomic indications and a lateral parapatellar approach.
Pennington et al. [36
] described technical considerations for performing LUKA. They included what they described as unique tibial component positioning to allow for the screw-home mechanism. Using a lateral parapatellar approach, they described internally rotating the tibial component 10° to 15°. They demonstrated this in their article using a plastic Sawbones®
]. Intraoperatively, while not always mandatory, using the vertical patellar tendon split to perform this internal rotation maneuver may be more reliable and easier (Fig. ).
While we used a fixed-bearing design in all cases, surgeons also use mobile-bearing implants for LUKA. Gunther et al. [22
] reported on 53 LUKAs performed with the Oxford implant. At an average followup of 5 years, survivorship was 82%, with 11 implants having a revision. These authors had a 10% incidence of bearing dislocation. They concluded mobile-bearing implants are a poor choice for LUKA [22
]. This high rate of mobile-bearing dislocation is reportedly due to the posterior femoral translation of the lateral femoral condyle during flexion [5
]. In a subsequent study [34
], the authors used a novel domed tibial plateau implant, and the rate of mobile-bearing dislocation was only 1.7%. Whether a mobile-bearing design used laterally will yield the same long-term survivorship and low wear rate as those of mobile-bearing MUKA remains to be seen [26
]. Longer followup of our series is necessary to determine whether wear and loosening of a fixed-bearing device result in failure.
In conclusion, by using a lateral parapatellar approach with the vertical tibial resection performed through the patellar tendon, we achieved a 1% revision rate and 3% reoperation rate. We utilized isolated lateral bone-on-bone arthrosis and maintenance of medial joint space either radiographically on a varus stress radiograph or arthroscopically as the indications for LUKA.