Abstract
Introduction
Early complication post total knee replacement reported to be higher in obese patient in general. Also the outcome of cruciate retaining and PS knee has been fully discussed before and there was no major difference in the outcomes for all the patients overall regardless of their weight. However, the purpose of this paper is to find out if the CR knee has superiority over PS knee in terms of clinical and functional outcomes and if early complication postTKR such as fracture and instability is more common in PS implant than in CR knee. This is a retrospective study comparing two groups of obese patients. The first using PS implant and the other using CR implant. These two groups were matched for age, body mass and severity of deformity.
Materials & Methods
At our institution we have been using Persona implant which has the option of using PS insert or a CR. The decision to proceed with CR or PS mainly depends on the availability of the implant and also the ability to well balance the knee in patients. In most patients we try to proceed with CR implant. However, the flow of implant sometime sometimes limit us from using CR or the imbalance in the ligament force us to process with PS implant.
We have reviewed a chart of over 200 patients in each group of obese patient they were done within the last three years. All cases had a minimum follow up of 6 months. Those groups were matched for body mass, age and severity of deformity.
After matching the groups we documented Knee Society Score (KSS), Knee Society Function Score (KSFS), blood loss, post – operative pain and complications. All surgeries were performed by the same surgeon.
Results
Our study showed that the clinical scores (KSS) in both groups were very close while significant differences were observed in functional scores (KSFS) for the CR knee.
We had 8 cases of per-prosthetic fracture in the PS group and one in the CR implant. We had 4 revisions in the PS group for instability and MCL insufficiency and non in the CR implant.
Infection, wound complication, blood loss, and patient satisfaction were same in both groups.
Discussion
This study suggests a significant difference in functional outcomes, especially walking, stair climbing and the use of walking aids, between CR and PS that favors CR implant which may be related to the CR knee retaining proprioception and ligaments tension with balance. In addition, PS knee have more varus-valgus and mid-flexion laxity than CR knee throughout the range of motion which appear clearly in obese patient.
On the other hand, the study clearly shows that the decrease incidence of peri-prosthetic fracture in the CR implant which could be easily explained by the fact that a good cortical bone is resected in order to make room for the PS spine. Also, the fact that resecting the posterior cruciate ligament might cause more stress on the implant versus the CR. Instability also were more common in the PS group. We believe this has to do with the fact that the PCL serve as a secondary constraint to the MCL. The presence of the PCL help maintain the stability in case of incidental injury to the MCL during surgery which was reported to be higher in obese patients.
Conclusion
There is clear advantage of improving the outcomes or knee scores and decreasing the early postoperative complications in obese patient using CR knee and we strongly recommend using CR implant in obese patients in order to restore functionality faster and reduce the incidence of peri-prosthetic fracture and the revision for instability.
