1 Background

Recent data projects an increased demand for TKA upwards of 400 % by the year 2040 3. Valgus deformity of the knee comprises upwards of 15 % of the deformities in primary total knee arthroplasty (TKA) patients.^1,2

Restoring appropriate alignment and maintaining stability can be challenging in valgus knee deformity. Defined in stages by Ranawat et al.² using the Tibio-Femoral Angle (TFA) and medial collateral ligament (MCL) status, valgus deformity results from excessive wear of the lateral bony structures of the knee with the potential for attenuated medial and lateral soft tissues.

The two implants most commonly used in TKA are posterior stabilizing (PS) and cruciate-retaining (CR) implants. Posterior stabilizing implants sacrifice the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) and provide stability through the cam of the femoral prothesis and tibial post. However, cruciate-retaining implants maintain stability and kinematics through retention of the native PCL. Although both are unconstrained implants, increasing degrees of constraint can be added through various polyethylene tibial plate inserts. Historically, PS implants have been favored for TKA in valgus deformed knees due to the assumption that even if the PCL is retained, it may be too incompetent to provide adequate stability.⁴ Revision rates in primary CR TKA for valgus deformity have been reported as high as 8 %.⁵

However, CR implants may improve proprioception and stability with less bony resection compared to PS implants.^6,7 Although there is evidence for the performance of CR implants in primary TKA with valgus deformity, aggregate understanding is needed to provide guidance to surgeons.

The purpose of this systematic review is to aggregate findings for cruciate-retaining implants used in primary TKA in valgus deformed knees. Secondarily, we aim to describe gap balancing techniques when using CR implants.

2 Methods

3 Results

3.1

3.1 Query results

Following irrelevant exclusions, 29 full text studies were screened, of which eight aligned with the inclusion criteria (Fig. I). Of the 22 excluded studies, 12 failed to stratify results by prothesis, seven failed to stratify results by deformity and two performed an intraoperative deformity correction in addition to primary total knee arthroplasty.

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Fig. 1 Flowchart summarizing the database search return, assessment, and final selection including specific exclusion criteria.

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4 Discussion

Studies indicate that valgus deformity comprises approximately 10–15 % of primary total knee arthroplasties.^1,2 With the incidence of primary TKA projected to increase over 400 % by 2040, a more complete understanding of primary TKA in valgus deformity has important implications. The use of CR implants has continued to steadily increase over the last decade, compromising over 50 % of TKA implants.¹⁷ Advantages of CR implants include reduced bone resection, and preservation of the PCL which may aid in joint proprioception and elimination of patellar clunk syndrome.¹⁸ Our results across 710 cases of CR primary TKA demonstrate satisfactory function with concerning rates of revision.

The PCL is the primary restraint to posterior tibial translation to prevent knee hyperflexion.⁷ If competent and retained, the PCL can provide stability and maintain native function, potentially improving outcomes. Valgus deformity increases the risk of peroneal nerve and surrounding soft tissue injury during TKA. Further, prolonged deformity may lead to contracture of the peroneal nerve which can complicate surgical management and the recovery course. The nerve is in close proximity to the tibia cut and may be inadvertently injured during extensive lateral soft tissue manipulation or release. A joint line that is excessively elevated may cause a traction injury on the already contracted nerve.^19,20 Pang et al.²¹ demonstrated superior functional outcomes and a more native joint line in unconstrainted CR implants in primary TKA in valgus knees when compared to constrained condylar knee (CCK) implants. Additionally, Ang et al.¹³ reported that PS and CR implants performed comparably at 24 months in valgus deformity TKA. Additionally, the authors noted that PS implants had a significantly higher incidence of radiographic anteroposterior laxity at one year postoperatively which was potentially attributable to PCL resection.

Component position is critical in valgus deformity due to the inherent alterations in stabilizers. Jonsson et al.²² detailed the increased risk of component malposition and malrotation in valgus deformed knees due to the hypoplastic lateral femoral condyle and possible relative tibial external rotation. Thus, accurate bone cuts and guide alignment are crucial while attempting to correct the valgus deformity. Slevin et al.²³ reported that increased valgus alignment of the TKA femoral component demonstrated increased bone tracer uptake in the patella which can contribute to pain and unsatisfactory outcomes. The current investigation elucidated a temporal trend for patella resurfacing in the more recent studies. In 116 cases of CR primary TKA, Chun et al.²⁴ reported no significant difference in outcomes between patients with and without patellar resurfacing.

Chronic valgus deformity leads to contracted lateral soft tissue structures which attenuates the medial structures. This is contrary to the native anatomy which is relatively lax laterally. A valgus deformed knee can be balanced by release of the tight lateral structures or reconstruction of the lax medial structures. Selective sequential release of lateral structures most commonly occurs after bone cuts when the knee is stressed and taken through range of motion with the trial implants. Gap balancing is performed as needed. The literature demonstrates heterogeneity in gap balancing sequence and technique. In the late 1990s Whiteside²⁵ reported outcomes and release techniques for TKA in valgus deformity. Over 80 % of the series was tight laterally in flexion and extension with around 1/3 of these only requiring release of the popliteus tendon and lateral collateral ligament (LCL). Another 1/3 required release of the iliotibial band (ITB) in addition to the popliteus and LCL. The remaining patients required additional release of the lateral capsule to achieve balance in extension. The LCL and popliteus tendon were released directly from bone, maintaining attachments to synovium and synovial membrane. This loosened the lateral knee but did not completely remove their stabilizing function. Similarly, the ITB was released “extrasynovially”, retaining proximal and distal attachments to synovial membrane.

More recent reports by Koskinen et al.¹² and Matar et al.²⁶ described pie-crusting of the ITB then popliteus tendon before progressing to deeper structures. This is consistent with the pie-crusting release technique reported by Aglietti et al.²⁷ which began with the posterolateral capsule then involved the LCL and ITB as needed. Medial reconstruction can also be performed either in conjunction with or independent of lateral soft tissue releases to achieve adequate gap balancing.^4,28,29 A constrained polyethylene insert can improve stability, mitigating the lax MCL which is common in valgus deformity. In aggregate, there is no standardized protocol for gap balancing in valgus deformity primary TKA. The surgeon should be mindful of the function of each structure in flexion and extension to guide the balancing process.

Instability is consistently reported as one of the most common indications for revision TKA. Preoperative alignment and implant choice have been identified as contributors to instability leading to failure.³ Intraoperatively, if the PCL is deemed incompetent, CR implants should be avoided as they may increase the risk of instability and need for revision.³⁰ Similarly, Berend et al.³¹ concluded that CR implants in valgus deformed knees had an increased risk of failure due to ligament imbalance.

Revision total knee arthroplasty is projected to increase over 180 % by 2030.³² Savov et al.⁵ reported all-cause revision of 10.5 % at a mean follow up of 57 months for CR TKA in valgus deformity. Our study reports 8.3 % all-cause revision at a mean follow up of 78 months. Both values reflect a substantially higher rate than the 4.2 % revision rate in 60,546 patients from 2007 to 2016 with CR implants at 8 years follow-up reported by Spekenbrink-Spooren et al. in the Dutch Arthroplasty Register.³³ Similarly, the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), reported an all-cause revision rate of 5.5 % at 10 years follow-up in 139,233 patients with CR implants.³⁴ Elevated rates of revision may be attributed to technical difficulties managing soft tissue tension leading to instability. Our results depict a temporal trend in revision rates. The two of the three most recent studies^5,12,26 reported zero all-cause revisions at an average of 49 months follow-up. Albeit a small sample and short follow up term, this finding is compelling and may be due to improvement in implant design or surgical technique.

We acknowledge several limitations to our current study, including those inherent to systematic reviews. Primarily, our work is limited by the methodology of the included studies. The changes in surgical technique and implant design across a wide time frame will have an effect on outcomes. Though it is reasonable that this temporal span of investigation improves the generalizability of the findings. The heterogeneity of reported outcomes reduces the applicability of our findings. The mean follow-up of the reviewed studies indicates that a majority of the patients were only followed for less than 10 years, which is a mid-term of follow up. It is unclear whether the current findings will remain consistent across the long-term. All studies provided detailed reporting of revision which may be one of the most important factors in the evaluation of CR implants for valgus TKA. There was variance in gap balancing steps and technique, indications for soft tissue release and for patella resurfacing. These factors and implant design vary across a wide time frame and are likely to impact outcomes. Though it is reasonable that the temporal span of investigation improves the generalizability of the findings.

5 Conclusion

This literature review demonstrates that cruciate-retaining primary total knee arthroplasty in valgus deformity provide satisfactory functional outcomes; however, rates of revision were higher in this population compared to aggregate reporting for the general population.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Ethical statement

This research did not require IRB approval.

Patient consent

This research did not require patient consent.

CRediT authorship contribution statement

Peter A. Falgiano: Conceptualization, Methodology, Investigation, Data curation, Writing – original draft, Writing – review & editing, Project administration. John J. Heifner: Methodology, Investigation, Data curation, Writing – original draft, Project administration. Thomas O. Yergler: Methodology, Investigation, Data curation, Writing – original draft, Project administration. Christopher Guerra: Methodology, Investigation, Data curation, Writing – original draft, Project administration. Arturo Corces: Conceptualization, Methodology, Investigation, Writing – original draft, Writing – review & editing, Project administration.