Initially the same components were used for both medial and lateral unicompartmental replacement. The results on the lateral side were, however, disappointing with a dislocation rate of about 10% (Gunther et al., 1996). The reason for the high dislocation rate was that the lateral collateral ligament is loose in flexion (Fig 1.10). In contrast, the medial collateral ligament is tight in all positions. Over the years, many improvements to the implants and the surgical technique for lateral arthroplasty have been introduced with a steady improvement in results. The current iteration (Fig. 1.11), which involves a convex domed tibial plateau and biconcave bearing implanted through a lateral parapatellar approach, has reduced the dislocation rate to a level that is acceptable although it is still higher than that achieved on the medial side and is therefore only appropriate for surgeons experienced with the Oxford Knee. Less experienced surgeons are advised to use fixed bearing UKA laterally. The surgical technique is very different from that used on the medial side. Because lateral unicompartmental replacement is less common than medial UKA, the domed lateral Oxford Knee is only performed by a limited number of surgeons. However, with further improvements, we expect the dislocation rate to decrease further and the use of the domed lateral to increase.
Figure 1.10 Distraction of the lateral compartment in normal flexed valgus-stressed knee. (Reproduced with permission and copyright © of the British Editorial Society of Bone and Joint Surgery [Tokuhara Y, Kadoya Y, Nakagawa S, Kobayashi S and Takaoka K. The flexion gap in normal knees. An MRI study. J Bone Joint Surg [Br] 2004; 86-B: 1133–6].)
