Rationale

Understanding the laxity of the collateral ligaments of the native knee, in extension and flexion, may help surgeons to avoid undesirable outcomes following TKA. It may allow for the improvement of implant designs and for the modification of surgical techniques to better restore or preserve the tension of native ligaments.

Clinical comment

With the traditional use of nonanatomical alignment methods and implants in TKA, it is unknown whether the ligament laxities following TKA should replicate the values observed in native knees in order to provide improved knee function, patient satisfaction, and implant survivorship.

Available literature and quality of the evidence

Nine studies that evaluated laxities of the collateral ligaments in the arc of motion of normal knees were identified. These studies are descriptive in nature, using a limited number of living subjects, cadaveric specimens, or reconstructed three‐dimensional (3D) models. Quality of evidence: level IV. Moreover, protocols and methods to assess the ligaments’ behavior were very different from one study to the next.

Findings

Both collateral ligaments were found to be tighter in extension than in flexion. Comparing both collaterals in extension, a looser lateral collateral ligament (LCL) was reported. This difference in side‐to‐side LCL laxity increased with greater flexion.¹–⁹ During knee flexion, a tighter medial collateral ligament (MCL) with a laxer LCL results in posterior translation of the lateral condyle over the lateral tibial plateau, creating internal rotation of the tibia with a medial pivot center of rotation.⁴,⁷,¹⁰–¹² This internal tibial rotation allows higher postoperative knee flexion¹³ and reduces pressure on the patella.¹⁴,¹⁵ In papers comparing males and females, females tend to have laxer ligaments than males.¹–⁸,¹⁰,¹⁶

Many authors evaluating collateral ligament laxities identify that MCL tightness plays a major role in native knee function and stability.⁴,⁷,¹⁰–¹² In addition to its function as the major valgus stabilizer, the deep MCL has a significant role in knee rotational stability, especially with a ruptured or sacrificed anterior cruciate ligament (ACL).¹⁴,¹⁶–¹⁸ The knee’s collateral ligaments laxities are rarely modified in knees with less than 15° of deformity.¹⁹ The biomechanics of a knee that has undergone TKA are different from those of a normal knee. It is therefore unknown if ligament tension values aimed for during TKA should be the same values that are measured in normal knees. Some authors suggest that medial soft tissue releases or femoral component external rotation may loosen the MCL and affect TKA outcomes.⁹,¹⁴

Resolution of clinical scenario

• In normal knees, both collateral ligaments are tighter in extension than in flexion, with the LCL laxer than the MCL with increased flexion.
  
• The MCL plays a major role in valgus and rotational knee stability, especially in the presence of a deficient or sacrificed ACL.
  
• Medial soft tissue releases when performing a TKA, which leads to increased MCL laxity, which may have a significant impact on postoperative knee function.

Rationale

TKA with mechanical alignment (MA) may not replicate collateral ligament laxity/tensions observed in the native knee. Often, surgeons must perform collateral ligament release to adjust the mediolateral (M/L) and flexion/extension balance. Is there clinical evidence that a certain level of collateral ligament laxity and M/L or flexion/extension imbalance would impact patients’ function and satisfaction?

Clinical comment

Understanding the postoperative correlation between ligament balance and clinical results may help surgeons to improve their surgical technique, thereby improving their patients’ results.

Available literature and quality of the evidence

• 1 level III and 4 level IV studies that evaluated the correlation between ligamentous laxity and clinical and functional outcome were identified in the literature.
  
• 2 level IV studies that evaluated the extent of acceptable ligamentous laxity were also identified.

Findings

Knee instability after TKA is considered the second most common cause of revision surgeries, with rates varying from 21 to 35%.²⁰,²¹ An unbalanced knee is defined as failure to balance the soft tissue envelope to obtain a rectangular flexion and extension gap. Residual imbalance was associated with loosening, polyethylene wear, and failure.²²,²³

Looking at the relation between patient outcomes measured by clinical scores and ligament balance, an M/L gap difference of <3 mm, using an intraoperative tensor and navigation, provided better Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores than larger gaps (84.9 ± 18 vs 74.8 ± 20.8, p = 0.017) in 108 TKA patients.²⁴ Using a knee balancer in 526 TKAs and defining the unbalanced knee with an M/L difference of more than 3°, a significant difference was found between balanced and unbalanced knees regarding the change in the clinical rating knee score for the extension and flexion balance (t‐test, p = 0.046; and ANOVA, p = 0.001, respectively). On the other hand, the authors did not find a significant difference in the change in the Oxford Knee Score.²⁵

In a multicenter study involving 176 TKAs, the use of intraoperative pressure sensors helped distinguish balanced from unbalanced knees. Balanced knees were defined as having M/L intercompartmental loading difference ≤15 lb through a range of motion. At six months postoperatively, balanced patients showed significantly better WOMAC (14.5 vs 23.8, p = 0.0001) and Knee Society Score (KSS) scores (172.4 vs 145.3, p = 0.0001) compared to unbalanced knees.²⁰ Conversely, a study comparing medial/lateral compartmental force ratio and total contact force found no correlation with functional scores at one year in a cohort of 101 TKAs.²⁶

Regarding range of motion and ligament laxity, in a study of 63 TKAs, 78% of slightly loose knees reached more than 100° of flexion compared to 62.5% of tighter knees.²⁷ Evaluating bilateral TKA patients with different postoperative contralateral laxities (evaluated with stress radiographs, >3° opening was considered loose), 10/11 patients preferred the loose side compared with 11/22 who preferred the other side (p <0.05).²⁸ Evaluating anteroposterior laxity at 75° of flexion in 93 TKAs, patients with knee laxity >10 mm had significantly inferior KSS (77.0 vs 55.3, p = 0.05) and knee flexion (99° vs 112°, p = 0.01).²⁹

Computer navigation may be predictive of the need for ligament release and may reduce systematic over‐release.³⁰

Related posts:

The Direct Anterior Approach Patient‐Specific Instrumentation in Total Knee Arthroplasty Management of Glenoid Bone Loss Distal Femur Fractures Periprosthetic Fractures: Knee Lisfranc Injuries

Stay updated, free articles. Join our Telegram channel

Join