Examination of the Knee Before and After Total Knee Replacement

Raj K. Sinha, MD, PhD

INTRODUCTION

This purpose of this chapter is to discuss the examination of the knee as it pertains specifically to total knee arthroplasty (TKA), rather than to be an exhaustive treatise on knee examination relevant to other surgical procedures. Although the examination of the soon-to-be-replaced knee is relatively streamlined, almost every pertinent finding has an important impact on planning and executing the knee replacement. Similarly, after knee replacement, particularly in an unhappy patient, examination is as important as imaging and other tests to help determine the etiology of an unsuccessful replacement. In the case of the happy knee replacement patient, of course, examination and imaging are usually both satisfactory!

EXAMINATION OF THE KNEE BEFORE KNEE REPLACEMENT

Inspection and Observation

Skin

As knee replacement will require a surgical incision, integrity of the skin is critical for a successful outcome. The skin at the surgical site should be healthy, without lesions, with excellent flexibility, vascularity, and turgor. In the case of inflammatory conditions such as psoriatic arthritis, all rashes should be optimized prior to surgery. The author employs the assistance of a rheumatologist or dermatologist to achieve this. When recent trauma has occurred, all ecchymosis and induration should be allowed to heal prior to surgery. Similarly, conditions such as prepatellar bursitis may affect the decision to proceed with TKA. For example, the prepatellar bursa may be so tense that the overlying skin appears compromised. The concern arises that healing may be delayed after surgery, thus unnecessarily raising the risk of infection in TKA. In such cases, the author has performed a bursa excision, in effect as a sham incision, to confirm that healing will proceed normally. Likewise, if vascularity is thought to be compromised, performing a sham incision is a reasonable approach before proceeding with knee replacement.¹ The use of transcutaneous pO₂ to assess vascularity has shown to be of some value, as areas of lower oxygen tension may demonstrate delayed healing.² Thin skin, especially in the obese and elderly, is prone to persistent wound drainage and may require special closure techniques³ (Fig. 15-1A). Of course, knee replacement should never be undertaken in the face of surgical site cellulitis or other infections.

A common situation encountered in TKA patients is previous surgical incisions. Prior arthroscopy, open meniscectomy and repair of fractures about the knee are quite frequent prior to TKA. The location of these incisions should be noted, particularly whether they will affect the TKA incision. In general, the most recent or most lateral incision should be utilized⁴ (Fig. 15-1B), as the lateral side of the skin tends to be more hypoxic after surgery. Similarly, the longitudinal TKA incision should cross more transverse incisions as perpendicular as possible. Oblique incisions can frequently be extended proximally and distally, still allow excellent joint exposure, and result in a more cosmetically pleasing scar (Fig. 15-1C and D). Fortunately, in the last several decades, as TKA became a more reliable salvage solution after trauma, midline skin incisions have become more popular for fracture fixation, resulting in fewer issues for the arthroplasty surgeon. In cases of multiple incisions, with excessively scarred and immobile skin, pre-TKA tissue expanders can be utilized.⁴ In conclusion, the condition of the skin is of paramount importance to an eventual successful outcome.

Gait

Evaluation of the patient’s gait will demonstrate varus or valgus thrust, varus or valgus joint alignment, hip/spine/foot/ankle issues, and muscle strength. Dynamic thrust during gait is predictive of asymmetric joint loading and cartilage wear,⁵ and the demonstration of a thrust helps to confirm the presence of advanced joint degeneration (Fig. 15-2A to C). Similarly, the degree of static varus or valgus alignment is reflective of degree of cartilage and/or bone loss. In terms of relevance to TKA surgery, thrust may indicate ligamentous laxity, whose presence may determine implant choice or adjustment in reconstruction technique. Thus, the presence of dynamic or static thrust necessitates a thorough examination of knee ligament functionality. Abnormal gait may also reveal hip/spine/foot/ankle pathology. Prior to proceeding with TKA, it is important to determine whether issues with other ipsilateral or contralateral joints may affect technique or
postoperative rehab. For example, when severe hip joint osteoarthritis is present, total hip arthroplasty should be performed before TKA. Abnormal muscle strength may manifest in an abnormal gait pattern and should be addressed when considering TKA. A weak quadriceps will result in a forward lurch and may be indicative of an underlying neuromuscular condition or myopathy, both of which would affect rehabilitation after TKA. Thus, evaluation of gait will help the arthroplasty surgeon customize the knee reconstruction and possibly adjust the treatment plan to avoid a complication and optimize the outcome.

FIGURE 15-1 A: Thin skin, concerning for delayed postoperative healing or slough from postoperative swelling. B: Example of a knee with previous multiple incisions. In this case, the incision marked with the arrow would be most favorable for total knee arthroplasty (TKA). C and D: Example of a TKA performed incorporating a previous surgical scar. Preoperative (C—scar marked by line). 1 y postoperative (D).

Deformity

INTRA-ARTICULAR

Within the joint, varus or valgus deformity can occur from cartilage loss, bone loss, malunions, ligamentous laxity, or some combination of all. Each of these parameters will affect the surgical reconstruction. For example, bone loss may necessitate the use of stems or wedges to create the proper joint line position and angle. Similarly, collateral ligament incompetence may require a more constrained polyethylene insert or even a hinged arthroplasty. Combined with imaging, physical examination will assist in planning the reconstruction.

FIGURE 15-2 A: Example of valgus deformity. B: Same patient standing and taking a forward step. Note the increase in valgus alignment or valgus thrust. C: Corresponding X-ray with weight-bearing. Note lateral collapse with medial opening, suggestive of possible loss of medial collateral ligament integrity.

EXTRA-ARTICULAR

Deformity in the femur or tibia, from a congenital condition or prior trauma, will also affect the TKA reconstruction. Old fractures or excessive bowing of bones may compromise the use of intramedullary instruments for alignment. Malunions leading to leg length inequality may require shoe lifts to aid in rehabilitation and walking post reconstruction. With modern tools such as surgical robots, prenavigated instruments, customized patient-specific implants, and intraoperative surgical navigation, the surgeon should be able to successfully lessen the overall effect of extra-articular deformity on the surgery itself. However, consideration of the deformity will aid in postoperative recovery.

Palpation

RELEVANT BONY LANDMARKS

All the bony landmarks of the knee joint should be palpated during the examination. This includes compressing the patella in extension to assess for hypermobility and retinacular asymmetry (Fig. 15-3A and B). At 30° of flexion, the patellar facets contact the femoral trochlea. Compression at this flexion angle will indicate abnormal patellar tilt or maltracking, if present, as well as degree of pain (Fig. 15-3C and D). Tilt and tracking may affect patellar component position or the decision to perform a lateral retinacular release during surgery. The absence of pain may open the consideration for unicompartmental arthroplasty or leaving the patella unresurfaced during TKA in the proper clinical setting. On the femur, both condyles and epicondyles and the menisci should be examined. Condylar tenderness may suggest bone marrow edema. Epicondylar tenderness may suggest collateral ligament injury. Meniscal integrity is not important to TKA since the menisci will be excised. However, meniscal injury may contribute to some other mechanical instability. The fibular head should also be palpated to assess the lateral collateral insertion as well as whether the peroneal nerve may be entrapped or tethered. The medial tibial plateau should be palpated to assess the medial collateral ligament (MCL) insertion and pes anserine bursa. Pes tenderness may indicate a combination of weak quadriceps and tight hamstrings. Palpation of the lateral plateau, including Gerdy’s tubercle, will assess the iliotibial band (ITB) insertion. The ITB, along with the collateral ligaments, imparts stability to the joint in full extension, both before and after TKA.

Ligament Integrity and Stress Testing

ANTERIOR CRUCIATE LIGAMENT

Until recently, the anterior cruciate ligament (ACL) was sacrificed in all TKA surgeries. The recent introduction of ACL-posterior cruciate ligament (PCL) retaining TKA designs has been met with marginal success.⁶ At the current time, ACL integrity is essentially irrelevant to TKA, although ACL dysfunction may contribute to posterior medial bony erosion.

POSTERIOR CRUCIATE LIGAMENT

TKA designs that retain the PCL (CR-TKA) remain popular in North America. If the surgeon is planning a CR-TKA, then obviously the PCL must be intact and functional for the TKA to be stable. The PCL can be assessed with a “posterior” Lachman’s test and with a
posterior drawer test (Fig. 15-4A and B, respectively). In the former, with the patient supine, the knee is flexed to 30° and a posterior force is applied to the tibia. In the posterior drawer test, with the patient supine, the knee is flexed to 90°, and a posterior force is applied to the tibia. In both tests, there will be a firm end point if the PCL is intact.

FIGURE 15-3 A: Examination of patella in extension. The examiner’s thumbs push the patella medially to check for lateral retinacular tightness. B: Examination of patella in extension. The examiner’s forefingers push the patella laterally to check for medial tightness. C and D: Examination of patella at 30° flexion demonstrating lateral tilt (C) and lack of movement medially (D).

MEDIAL COLLATERAL LIGAMENT

In all primary TKA designs, the MCL is critical for medial-sided stability. The MCL should be assessed at full extension and at 30° of flexion (Fig. 15-5A and B). In both positions, a valgus stress is applied to the tibia while the femur is held stably. At full extension, both the posterior capsule and MCL contribute to medial side stability and resistance to valgus stress. At 30°, the posterior capsule relaxes, and only the MCL acts as a restraint to valgus force. If there is no medial opening at 30° with valgus force, then the MCL is likely contracted or tethered by osteophytes. This information will help the surgeon determine how aggressively to release the medial side during surgery. (It should be noted that in a fixed varus deformity, the five attachments of the semimembranosus tendon frequently contribute to the varus contracture and deformity and may have to be released during surgery.) If the knee corrects to a neutral position only, then the MCL is intact and is not contracted or tethered. In addition, bony integrity on the lateral side is also preserved. Thus, the medial release required should likely be minimal at the time of surgery. If the medial side opens with no clear-cut end point, then the MCL is likely incompetent or there is severe lateral bony compromise. Not only will release be unnecessary, but also increased implant constraint or bony augmentation may be necessary.

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