Elsevier

The Knee

Volume 20, Issue 6, December 2013, Pages 407-411
The Knee

Total knee arthroplasty with patient-specific instruments improves function and restores limb alignment in patients with extra-articular deformity

https://doi.org/10.1016/j.knee.2013.07.001Get rights and content

Abstract

Background

Restoring function and alignment when treating knee arthritis with a total knee arthroplasty (TKA) in patients who have an extra-articular deformity (EAD) from a malunion or with retained femoral hardware is a challenge. The normal anatomical landmarks are hard to find and difficult to use to obtain correct alignment. The procedure will be further challenged by angular deformity of the femur or tibia. A retrospective study was performed on a case series of patients with EAD or obliteration of the canal treated with patient-specific instruments (PSI).

Methods

A multicenter retrospective review of 10 patients with multiplanar deformities in which the knee components were aligned with patient-specific instruments was performed. Outcome and alignment were studied.

Results

At a mean follow-up of 3.4 years, function improved from preoperative as evidenced by a mean increase in the KS pain score of 53 points, KS function score of 48 points and Oxford Score of 28 points (P < 0.05). Flexion improved from 94° +/− 11° to 112° +/− 15° (P < 0.05). Limb alignment was restored with a mean Hip-Knee-Ankle angle of 179.3° +/− 1.3° (P < 0.05). Maximum outliers were 177° to 181°. An average tourniquet time of 75 +/− 9 minutes (range, 62–83 min) was observed.

Conclusions

The use of patient-specific instrumentation systems to perform TKA in patients without access to the intramedullary canal because of EAD or fixation devices, improved function and restored limb alignment. Mechanical alignment can easily be obtained with this technique by intra-articular correction of deformities under 20°.

Level of Evidence

Level IV.

Introduction

Alignment is crucial in total knee arthroplasty (TKA) for implant survival and clinical outcome [1], [2], [3]. Both conventional instruments and computer-assisted navigation (CAS) have been used to obtain these objectives [4], [5], [6]. Intra-medullary (IM) instruments recreate the mechanical axis by using the anatomical axis and landmarks [1], [2], [3], [4], [5], [6], [7]. CAS is based on finding the center of the femoral head, the knee and the ankle allowing surgeons to find the mechanical alignment without using the anatomical axes [3], [4]. The use of these navigation systems has resulted in improved alignment [2] but has not completely eliminated outliers or improved clinical outcomes [9], [10]. The area where the advantages of CAS is clear, is in the presence of posttraumatic extra-articular deformities (EAD), retained hardware, ipsilateral long stem total hip arthroplasty or any situation where traditional instrumentation is not feasible [3], [4], [11], [12], [13].

Recently a new instrument for aligning the limb in all three planes, patient-specific instruments (PSI) using MRI or CT-scan, has been developed. Patient-specific positioning guides or cutting blocks are designed from radiological images and are supposed to allow surgeons to improve accuracy in the three planes or the six degrees of freedom of a knee implant [10], [14]. As with navigation, these instruments are based on direct mechanical alignment without using the anatomical axes [3], [4].

Extra-articular deformities have always been a challenge to obtain alignment either by corrective osteotomy or by intra-articular correction of the axis [4], [11], [15], [16]. For these special cases, navigation has proven to be of added value [1], [3], [4], [12], [17]. However, EAD cases can be even more challenging than standard TKA. These complex angular deformity cases ask for experience of the surgeon with the navigation system, especially with the finding of the anatomical landmarks and the technical aspects of correcting EAD via intra-articular resections [13], [17].

In a retrospective multicenter case series, the authors analyzed nine cases of extra-articular deformity and one case of femoral canal obliteration with an internal fixation device, operated with patient-specific instruments (PSI) and intra-articular correction of the alignment using primary implants.

The hypothesis of this study was [1] that PSI restores mechanical limb alignment in total knee arthroplasty with EAD and [2] that PSI assisted TKA for EAD restores function.

Section snippets

Materials and Methods

Between 2008 and 2010, ten patients (6 men and 4 women) with posttraumatic knee arthritis and femoral or tibial canal obliteration or deformity were operated for total knee arthroplasty by 3 of the authors (ET 6; MP 3; MH 1 case). All patients presenting during that consecutive period of time were selected for patient-specific instrumented TKA. At the time of surgery, the mean age of the patients was 58.5 +/− 8.5 years. The average BMI was 33.2 +/− 3.5 kg/m2. Obliterations of the canal were

Results

At a mean follow-up of 3.4 years (range, 2–5 years), the mean Knee Society function score increased from 44 +/− 11 points pre-operatively to 92 +/− 7 points postoperatively (P < 0.05). The mean Knee Society pain score improved from 38 +/− 6 points pre-operatively to 91 +/− 9 points postoperatively (P < 0.05). The Oxford Score improved from a mean 15.6 +/− 5 to 43.5 +/− 4 points (P < 0.05) (Fig. 1).

For all patients, the extension improved from – 7° +/− 3° (range, + 5° to - 11°) to 0° (range, + 2° to − 3°)

Discussion

The most important findings of this study were a statistical improvement in function from preoperative observed for all patients as evidenced by a significant increase in both Knee Society and Oxford Scores and a restoration of the mechanical alignment with PSI in EAD total knee arthroplasty.

Secondary findings of this study were that posttraumatic arthritis patients have reduced pre-operative flexion but that a significant amelioration in flexion can be obtained after TKA. However their

Conclusions

Patient-Specific Instruments are an alternative for conventional instruments and computer-assisted navigation for osteoarthritic knees with extra-articular deformities or retained hardware. Improvement in function and mechanical alignment were obtained at a minimal two years follow-up.

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