Unicompartmental knee arthroplasty (UKA) has been gaining popularity in recent years due to its perceived benefits over total knee arthroplasty (TKA), such as greater bone preservation, reduced operating-room time, better post-operative range of motion and improved gait. However there have been failures associated with UKA caused by misalignment of the implants that have lead to revisions. To improve the implant alignment a robotic guidance system called the RIO Robotic Arm has been developed by MAKO Surgical Corp (Ft. Lauderdale, FL), which is designed to give improved accuracy compared to traditional UKA using cutting jigs and other manual instrumentation.

The University of Strathclyde in association with Glasgow Royal Infirmary has undertaken the first independent RCT trial of the MAKO system against the Oxford unicompartmental knee arthroplasty – a conventional UKA used in the UK. Motion analysis was used in order to obtain a quantitative assessment of their movement. The results from a total of 51 patients (23 MAKO, 28 Oxford) that underwent a one year post-operative biomechanical assessment were investigated.

Motion analysis showed that during level walking the MAKO group achieved a higher knee excursion during the highest flexion portion of the weight bearing stage of the gait cycle (foot-strike to mid-stance) compared to the Oxford group (18.6° and 15.8° respectively). This difference was statistically significant (p-value = 0.03). Other knee excursion values that were compared were from mid-stance to terminal stance, and overall knee flexion. No statistically significant differences were seen in either of these measurements. A subsequent comparison of both MAKO and Oxford groups with a matched normal cohort (50 patients), demonstrated that there wasn't a statistically significant difference between the MAKO group and the normal knees during mean knee excursion from foot-strike to mid-stance (18.6° and 19.5° respectively, p-value 0.36). However the Oxford group, with a lower knee excursion was found to be significantly different to our normal control group (15.8° and 19.5° respectively, p-value < 0.001).

This suggests that the robotic-assisted knees behaved more similarly to normal gait during this phase of the gait cycle than those of the conventional group. While significant differences in gait were found between the Oxford and MAKO groups, further work is required to determine if this results in improved knee function that is perceptible to the patient.

Unicompartmental knee arthroplasty (UKA) has been gaining popularity in recent years due to its perceived benefits over total knee replacements, such as greater bone preservation, reduced operating-room time, better postoperative range of motion and improved gait. However there have been failures associated with UKA caused by misalignment of the implants.

To improve the implant alignment a robotic guidance system called the RIO Robotic Arm has been developed by MAKO Surgical Corp (Ft. Lauderdale, FL). This robotic system provides real-time tactile feedback to the surgeon during bone cutting, designed to give improved accuracy compared to traditional UKA using cutting jigs and other manual instrumentation.

The University of Strathclyde in association with Glasgow Royal Infirmary has undertaken the first independent Randomised Control Trial (RCT) of the MAKO system against the Oxford UKA – a conventional UKA used in the UK. The trial involves 139 patients across the two groups.

At present the outcomes have been evaluated for 30 patients. 14 have received the MAKO unicompartmental knee arthroplasty and 16 the Oxford UKA. Both groups were seen 1 year post-operatively. Kinematic data was collected while subjects completed level walking using a Vicon Nexus motion analysis system. Three-dimensional hip, knee and ankle angles were compared between the two arthroplasty groups.

Our initial findings indicate that hip and ankle angles show no significant statistical difference, however there is a significant difference (p < 0.05) in the knee angles during the stance phase of gait. Data shows higher angles achieved by the MAKO group over the Oxford.

It would appear from our early findings that the MAKO RIO procedure with Restoris implants gives at least comparable functional outcome with the conventional Oxford system and may prove once our full sample is available for analysis to produce better stance phase kinematics with a more active gait pattern than the conventional Oxford procedure.

Further work includes analysing the data obtained from the patients in a number of other activities. These include a full biomechanical analysis of ascending and descending a flight of stairs, sit to stand and a deep knee lunge. The high demand/high flexion tasks in particular may reveal if there's an advantage to using the MAKO procedure over the Oxford. If there is a direct correlation between alignment and patient function then this effect could be more significant in the more demanding patient tasks.