Meniscal injuries are common in patients with varus or valgus malalignment, but consensus is lacking as to when surgery should address the meniscal injury only and when it should be combined with an osteotomy. Several factors need to be evaluated to provide the most appropriate treatment in each case. Here we highlight the most relevant literature on the subject and suggest a rationale for surgical treatment.
The menisci and lower limb alignment are intrinsically linked in the distribution of forces across the knee joint.
Lower limb alignment should be assessed in each case of meniscal injury.
When meniscus tears undergo repair surgery, several factors should be considered to determine whether a concomitant osteotomy is necessary.
The most relevant factors to take into consideration are concomitant cartilage injuries, whether the meniscal injury is traumatic or degenerative, the meniscal tear pattern, and anterior cruciate ligament status.
The menisci and lower limb alignment both play a crucial role in load transmission across the knee joint. The meniscus distributes the mechanical load by increasing the contact surface area, sharing the weight bearing across the articular surfaces. Any loss of functional meniscal tissue alters this function and contributes to compartmental instability. Similarly, varus or valgus malalignment contributes to knee overload by altering the load distribution across the knee. As meniscal pathology is commonly combined with malalignment, both aspects should be assessed when evaluating meniscal injury. This study reviews and analyzes the most important aspects to be considered in this scenario and highlights indications for isolated and combined treatments.
Biomechanics of the menisci
The menisci distribute the load across the knee and also stabilize the joint during motion. However, because of the anatomic differences of the medial and lateral compartments, the biomechanical properties of the medial and lateral menisci differ. Although the medial compartments have a concave form, the lateral tibial plateau is smaller and more convex. The corresponding menisci are shaped to conform to these differences. Due to the convex shape of the lateral tibial plateau, this compartment is less congruent and the lateral meniscus transfers a greater load during weight bearing. As a result, any amount of meniscal tissue resection decreases the contact area and increases the peak loads transmitted to the tibial plateau. In a normally aligned knee, the lateral and medial compartments carry 42% and 58%, respectively, of the total load. However, due to its shock absorber property, the menisci transfer only 70% of the total load to the tibial plateau.
Biomechanics of lower limb alignment
The most relevant aspects of lower limb alignment in relation to the meniscus are those that comprise the coronal plane. Most studies in the literature have assessed alignment in osteoarthritis (OA) and only a few have done so in healthy young individuals. Bellemans and colleagues assessed lower limb alignment in healthy young adults without knee problems. They found a mean hip-knee-ankle (HKA) angle of 1.9° of varus (SD ±2.4) in men and an angle of 0.81° (SD ±2.1) in women. Sixty-six percent of men and 80% of women had an HKA between 3° of varus and 3° of valgus. A varus alignment of more than 3° was observed in approximately 32% of men and 17% of women. Conversely, valgus alignment of more than 3° was only seen in 2% to 3% of cases.
The aim of osteotomy is to shift the load to the nonaffected compartment. The contact pressure in the unloaded compartment depends on the degree of alignment correction and whether a varus or a valgus osteotomy is being performed. In any case, a 7° varus or valgus osteotomy could unload the affected compartment by up to 70%, matching that of the meniscus shock absorber effect.
Dealing with a problem of the meniscus or alignment?
As meniscus function and knee alignment are closely related, they must both be assessed when either of the 2 conditions is diagnosed. For the medial compartment, alignment is of paramount importance. There is an ongoing debate in the literature regarding OA progression and the effect of alignment. Sharma and colleagues found OA progression correlated with alignment, with significantly higher functional deterioration over 18 months when malalignment was greater than 5° either in varus or valgus. Thorlund and colleagues also reported that the load transfer changes after meniscectomy. They found knee load indices increased 12 months after arthroscopic partial meniscectomy (APM), indicating compartment overload. Alignment also has been implicated in OA progression after meniscus resection. Covall and Wasilewski found less joint space narrowing more than 5 years after medial meniscectomy in patients with a preoperative tibiofemoral valgus of more than 4°. Burks and colleagues found more joint space narrowing 15 years after partial medial meniscectomy for varus with less than 0° in HKA as the cutoff. In contrast, in a regression analysis of 500 patients more than 10 years after APM, Chatain and colleagues did not identify alignment as a significant factor in OA progression.
Varus alignment is also a risk factor for medial meniscus posterior root tear (MMPRT). Hwang and colleagues compared MMPRT with other meniscus injuries and found a mean of 4.5° (SD ±3.4) of varus in the MMPRT group and 2.4° (SD ±2.7) of varus in the group with other meniscal injuries.
Meniscal repair can also be influenced by lower limb alignment. Due to the mobility of the menisci and to the role of the menisci in load transmission, it seems logical that varus or valgus alignment might respectively affect the healing potential of a medial or lateral meniscus repair. Surprisingly, no studies have addressed this aspect in detail. Since the adoption of a more comprehensive approach to root repair and meniscus transplantation in recent years, our understanding of the influence of alignment on meniscus injuries has evolved. The etiology of posterior root injury differs between the lateral and medial menisci. The more mobile lateral meniscus posterior root is frequently injured in a traumatic event in a younger person, usually when an anterior cruciate ligament (ACL) injury occurs. In these circumstances, Okoroha and colleagues reported that malalignment might be a risk factor for a lateral meniscus posterior root tear (LMPRT). With a varus angle of more than 3°, they found a 5.2-fold increase of LMPRT. They also observed that a posterior tibial slope of more than 12° was related to a 5.4-fold increase of this LMPRT. These findings highlight the stabilizing effect of the lateral meniscus as a secondary constraint to anterior tibial translation and the internal rotational force in an ACL injury. In contrast, the more tethered medial meniscus posterior root injury is most often part of a degenerative process, with varus malalignment, overweight, OA, and gender being the most common risk factors.
Medial and lateral meniscus in varus and valgus aligned knees
Several investigators have reported clinical correlations between alignment and OA. However, the deleterious effect on the articular cartilage due to malalignment and meniscus injuries has been little studied, and the influence of alignment on the outcome after meniscectomy is controversial. Although some believe that malalignment compromises the result of meniscectomy, others have stated that the lower limb axis does not affect the outcomes. One of the main reasons for this controversy is that preoperative alignment was not considered in many long-term studies after meniscectomy, and therefore, it was not assessed as an independent risk factor influencing clinical outcomes or osteoarthritis progression.
The effect of meniscectomy on postoperative alignment has been better studied. Findings have revealed an increase in valgus alignment after lateral meniscectomy and also after medial meniscectomy. It seems that the deformity produced by the meniscectomy is influenced by the amount of resected meniscal tissue, but not by the preoperative alignment. The study with the longest follow-up to date, 40 years, analyzed the tibiofemoral angle modification after meniscectomy and showed that a meniscectomy led to malalignment in the corresponding tibiofemoral compartment. However, this effect was more pronounced after a medial meniscectomy leading to a varus knee than after a lateral meniscectomy leading to a valgus knee. The tibiofemoral angle, the magnitude of malalignment, and the range of motion were strongly correlated with both Ahlback and Kellgren and Laurence scores. Be that as it may, patient-reported outcome measures did not correlate with the degree of OA. In fact, long-term follow-up after arthroscopic partial medial or lateral meniscectomy showed progressive degenerative radiographic changes, with small or no significant negative effects on knee function. One possible explanation is that body mass index (BMI) and degenerative meniscal tears are stronger risk factors for these degenerative changes than the degree of malalignment. It is generally accepted that cartilage deterioration is more frequently observed after lateral meniscectomy than after medial meniscectomy. This higher deleterious effect on the articular cartilage after lateral meniscectomy could be due to the convexity of the lateral tibial plateau being compensated with a larger meniscus covering more area than in the medial compartment. Finite elements analysis supports these concepts, showing that the maximum stresses and strains occurred on the medial tibial cartilage after medial meniscectomy only in a varus knee. Conversely, the drop from before to after in the contact stresses and strains was higher in the lateral cartilage after lateral meniscectomy regardless of whether the lower limb had a valgus or varus alignment.
The increase in peak contact stress after loss of meniscal tissue is directly related to the amount of tissue resection. The volume of removed meniscal tissue should also therefore be considered at the time of the surgery, given that it affects long-term radiological and clinical outcomes both in the medial and lateral compartments ( Box 1 ).
Varus and valgus alignment tend to increase after medial and lateral meniscectomy, respectively.
This increment is more pronounced in the medial compartment.
The cartilage deterioration is more pronounced in the lateral compartment.
The deformity after surgery is more related to the amount of resected meniscal tissue rather than to the degree of preoperative alignment.
The deformity after surgery does not correlate with functional outcomes.
Brophy and colleagues studied different factors in patients with reconstructed ACL. They found that varus alignment was associated with articular cartilage status in the medial compartment but not in the lateral compartment. Medial cartilage status was also correlated with BMI, whereas lateral compartment chondral injuries were significantly associated with age. For both compartments, they observed a relevant association with meniscal status. Patients with previous partial meniscectomy showed higher rates of degenerative changes than patients with previous meniscal repair or no previous meniscal surgery. In view of these observations, in an ACL reconstructed knee,
Varus deformity is an independent risk factor for the development of medial osteoarthritis
The combination of medial meniscectomy and varus alignment could increase the risk of cartilage degeneration
Valgus deformity is a risk factor only for lateral OA when it is associated with advanced age or previous meniscectomy. In such patients, the association of medial meniscectomy and varus malalignment could increase the risk of cartilage degeneration.