Revision total knee arthroplasty: Importance of ligament balancing

Introduction

Total knee arthroplasty (TKA) is a relatively simple and straightforward procedure among knee surgeries. 

However, some surgeons misunderstand fundamental surgical principles, leading to early prosthesis failure. If the surgery fails, revision TKA is technically demanding, and its outcomes are generally inferior to well-performed primary TKA. Therefore, precise surgical techniques must be employed during primary TKA to prevent early failure.

In this article, we present a case in which improper ligament balancing, a fundamental principle, was overlooked, ultimately leading to early prosthesis failure.

 

Case : A 78-year-old female

 

A 78-year-old female who underwent primary TKA of right knee only five years ago, visited the outpatient clinic with complaints of gait difficulty, subjective instability, and intermittent locking knee. 

These symptoms were indicative of the so-called "jumping phenomenon" due to medio-lateral ligament imbalance. Revision surgery was necessary. 

Her X-ray showed old MCL avulsion fracture and subluxated prostheses. 

On the Bell-Thompson view, the coronal alignment was neutral, but a significant joint line obliquity was observed

Analyzing the cause of failure

Analyzing the cause of failure is crucial in all revision surgeries. In this patient, two major factors contributed to failure:

1. CR-Type Bearing

The patient had received a CR type bearing, which contrasts with the PS type. 

 1) Posterior-Stabilized (PS) type: Posterior cruciate ligamnet is Substituted. 

 2) Cruciate-Retaining (CR) type: Posterior Cruciate ligament is Retained.

CR type bearings were once preferred due to the theoretical advantage of preserving the posterior cruciate ligament (PCL), thereby maintaining proprioception post-surgery. However, in advanced osteoarthritic patients, the PCL is often non-functional, diminishing the longevity of the implant. Hence, CR-type bearings have gradually fallen out of favor among many surgeons today.

Nontheless, previous surgeon used a CR-type bearing, leading to anteroposterior (AP) instability despite the patient's PCL insufficiency, . 

 

2. Ligament Imbalance

A common misconception among surgeons is that bone cutting is the key to a successful TKA. While precise bone cutting is important, ligament balancing is the most critical factor for long-term implant success. Improper ligament balancing is a major cause of early failure, particularly polyethylene (PE) bearing wear.

In this patient, the old medial collateral ligament (MCL) avulsion fracture could be explained by two possibilities: 

(1) the surgeon misaddressed a pre-existing MCL avulsion Fx.

(2) the surgeon made an iatrogenic injury during surgery. 

In conclusion, 

AP and ML balancing were all failed, led to an imbalance in all directions.

 

Treatment Approach

Intraoperatively, early PE wear was observed with multidirectional instability of knee joint. However, the metal prosthesis was relatively intact.

A common temptation in revision cases is to replace only the worn-out PE insert if the metal implant appears intact. However, this approach is inadequate in this patients. I would repeat the same failure in the future.

 

Thus, whole prosthesis were removed and a full revision was performed.

Key steps included:

1) Addressing Joint Line Obliquity: Preoperative Bell-Thompson views showed neutral alignment but revealed varus joint line obliquity. To correct this, distal block augmentation was performed on the lateral femoral condyle, and additional cutting on the lateral tibial plateau was carried out.

2) Balancing the Flexion Gap: The flexion gap between the medial and lateral compartments was unbalanced, contributing to the jumping phenomenon of the medial compartment. To resolve this, the femoral prosthesis were internally rotated:

  (1) A block was augmented at the posterior medial femoral condyle.

  (2) Cement and screw augmentation were performed at the anterior chamfer of the lateral femoral trochlea.

3) Check the gap balance during all range of motion 

4) Check the patella tracking during range of motion 

 

Result

Postoperative X-rays confirmed well-corrected coronal alignment and joint line obliquity.

  

Conclusion

1. CR-type bearings do not ensure long-term implant longevity, particularly in patients with PCL insufficiency.

2. Ligament balancing is the most critical factor in achieving long-term success in TKA.

Proper primary surgical techniques can prevent the need for complex revision procedures, ultimately improving patient outcomes.

Hyo Yeol Lee, MD., PhD.

Department of Orthopaedic Surgery (Knee Surgery and Sports Medicine)

Chungbuk National University Hospital, Korea