The integrity of the collateral ligaments is critical to knee joint stability and proper kinematics following primary total knee arthroplasty (TKA). Instability following TKA can be the source of residual pain and swelling. It is also a leading cause of early revision following knee replacement surgery. Intraoperative ligament injuries during TKA is a relatively rare event that has been reported to occur in approximately 0.8% to 2.7% of the time. Failure to recognize and appropriately manage these injuries can compromise patient outcomes and implant survivorship. Therefore, the purpose of this chapter is to develop a systematic approach to the management of ligament injuries during primary TKA.
Anatomy and Biomechanics
In the knee, medial stability is contributed by the superficial medial collateral ligament (MCL), deep MCL, hamstrings, and posterior medial capsule, while lateral stability is provided by the lateral collateral ligament (LCL), iliotibial band, popliteus, and posterolateral capsule. Generally, the anterior structures provide stability to the flexion gap, while the posterior structures impact the extension gap.
Injury to the collateral ligaments results in loss of constraint in both the coronal and sagittal planes as well as rotatory instability. The tibiofemoral translation can be more pronounced when the posterior cruciate ligament is sacrificed. Instability due to iatrogenic collateral ligament loss is generally more pronounced in flexion, as the posterior capsule generally adds coronal knee stability when the knee is in full extension unless there is severe global instability or knee recurvatum from posterior capsular insufficiency. Consequently, patients generally complain of pain, sense of instability, and recurrent knee effusions with flexion activities such as stairs, getting up from a chair, and walking on uneven surfaces or terrains.
Intraoperative Medial Collateral Ligament Injury
The MCL is vulnerable to injury at various stages of the TKA procedure. First, during exposure, care should be taken when developing the medial soft-tissue sleeve over the anteromedial tibia. An adequate medial soft-tissue envelope, including the superficial and deep MCLs, is required for adequate exposure (i.e., subluxation of the tibia) and subsequent knee joint closure. The proximal tibial release should be carried around the medial tibia to the hamstring tendon insertion. It is important to remember that releasing up to the proximal 4 cm of the superficial and deep MCLs will not significantly affect medial flexion and extension gaps. Failure to do so can risk avulsion of the MCL, particularly in obese patients.
Another point during the procedure in which the MCL can be injured is during the tibial and posterior condylar resections of the knee. From a technical standpoint, protective retractors should be placed between the deep MCL and the bone and the saw blade should be angled away from the collateral ligaments when making these bone cuts ( Fig. 9.1 ). In order to accomplish this, the medial soft-tissue sleeve must be properly developed to ensure appropriate exposure and safe instrumentation. Finally, Sappey-Marinier and colleagues showed that increased valgus laxity was associated with over-resection of the tibia, exceeding 14 mm. In many ways, this illustrates the compounding of errors that can occur during a TKA procedure.
Recognition and Assessment of the Ligament Injury
The first step to proper management of any complication is prompt recognition. Signs of ligamentous compromise can include (1) sudden improvement in surgical exposure, (2) preferential and unexpected laxity of a compartment over another (i.e. medial laxity in a varus knee), and (3) mismatch between the polyethylene insert thickness and amount of bone resected. Generally, a high index of suspicion that something is either not normal or unexpected should prompt additional investigation.
A simple way to investigate is to place a laminar spreader between the medial and lateral compartments to look for an asymmetric opening or a severe mismatch between the medial and lateral gaps ( Fig. 9.2 ). A spacer block can also be used to assess gap symmetry. Once it is determined that there has been a medial collateral injury, the next step is to assess the zone of injury. An intrasubstance injury versus an avulsion injury off the tibia may require different management strategies. Other factors that can influence treatment choice include the integrity of the medial retinaculum and the quality of the injured ligament.