Knee Osteotomies

Introduction

Osteotomies around the knee play a pivotal role in the treatment and prevention of osteoarthritis. They are also used as concomitant procedures to other joint preservation techniques, such as meniscal transplantation and articular cartilage restoration, and in the treatment of ligamentous instability. As such, realignment procedures in both the proximal tibia, distal femur, and tibial tubercle are regularly performed using a variety of techniques, all of which have potential specific complications.

The choice of the most appropriate surgical procedure is key to addressing the underlying pathology and associated deformity. Classically, valgus osteotomies were performed in the proximal tibia using a lateral proximal tibial closing wedge technique; however, the trend has more recently shifted toward medial opening wedge techniques, as respective outcomes prove to be equal, but with a technically less demanding procedure. ^, ^, ^, ^, ^, Varus osteotomies are most commonly performed in the distal femur before idiopathic genu valgum is often caused by lateral femoral condyle hypoplasia. Therefore to restore a parallel joint line or to avoid producing joint line obliquity, either medial closing or lateral opening wedge distal femoral osteotomies (DFOs) are the procedures of choice in these cases. ^, ^, Tibial tubercle osteotomies (TTOs) are most often performed in isolation, but may also be used in conjunction with tibial or femoral osteotomies. They are used to address several forms of patella malalignment in cases of recurrent patellofemoral instability. Their main aim is to unload the patellofemoral joint secondary to chondrosis or other secondary changes associated with increased contact pressures or abnormal patella tracking. Less commonly, they are combined with tibial osteotomies to maintain physiological patella height in cases where a large coronal plane correction is required to unload the affected tibiofemoral compartment. ^, Surgeon preference and intrinsic patient factors, along with an individual assessment of perioperative risk, all play a substantial role in determining which type of osteotomy will be selected for treatment.

Because each method has its particular hazards and pitfalls, an individualized approach to each case is needed to improve overall outcomes and decrease the risk of failure. Evaluation of preoperative risk factors can help decrease complications. Moreover, understanding the potential intraoperative, as well as postoperative, complications can aid in preventing them and enables the surgeon to master the procedure.

This chapter will outline the different complications associated with osteotomies around the knee, identifying specific areas where complication risk may be mitigated, using case examples where appropriate.

Medical Complications

The incidence of medical complications following osteotomy around the knee varies. Complications include, but are not limited to, cardiopulmonary issues, deep infection (1.7%), chronic regional pain syndrome (CRPS) (1.3%), and deep venous thromboembolism (1.3%). Preoperative patient assessment including a detailed history, physical examination, and investigational diagnostic workup is essential for successful patient selection before osteotomy procedures. Proper preoperative medical assessment helps to identify and optimize medical comorbidities, or to appropriately counsel those patients at high risk of complications, such as smokers or diabetics. ^, ^, Thorough practice and cautious indications can potentially eliminate unnecessary operative risks. In those cases, where the specific risk be deemed to be too high, a nonoperative approach may be selected or an alternative procedure chosen.

Strategy 1: Medical and Physical Optimization

Smoking, increased body mass index (BMI), diabetes mellitus, excessive alcohol intake and illicit drug use, advanced age, poor bone quality, and reduced tissue perfusion have all been described as preoperative risk factors potentially leading to complications such as delayed union or nonunion, as well as surgical site infection. ^, ^,

Smoking status and diabetes mellitus have been identified as the strongest predictors of complications following high tibial osteotomy (HTO) or DFO. ^, ^, Smoking has been described as both a relative and an absolute contraindication of realignment osteotomy. It is essential that patients are appropriately counseled with regard to smoking cessation before surgical intervention. If there is a concern that smoking may commence postoperatively, a closing wedge technique may be more appropriate to potentially mitigate the risk of nonunion. Increased BMI has also been identified as a risk factor for postoperative complications. A BMI of 25 kg/m ² or more (as per definition by the World Health Organization) is thought to potentially increase the risk of delayed union or nonunion. ^, Weight management programs are often suggested as an option for nonoperative treatment in terms of load reduction and should also be considered as means of preoperative optimization in case an osteotomy is planned. Bariatric surgery, which has recently become a popular way to improve outcomes of total knee arthroplasty (TKA) in the severely obese, remains to be investigated as an addition to osteotomies. Moreover, as part of the preoperative assessment and health optimization, workup should include consultation for proper perioperative medical management of comorbidities such as diabetes, and prehabilitation to enhance physical fitness, range of motion, and strength. ^, ^, ^,

Failure to Achieve Desired Coronal Plane Correction

Under- or overcorrection have been shown to lead to early failure. However, proper preoperative planning of every osteotomy procedure can reduce the impact of these potential complications. ^, ^, ^, There is an ongoing discussion about the optimal postoperative coronal plane alignment for specific deformities and conditions. In cases of osteoarthritis, current consensus suggests that the weight bearing mechanical axis should pass through the knee between 50% to 62.5% of the medial to lateral tibial width, resulting in 3 to 5 degrees of mechanical valgus. The latter 62.5% position on the tibial joint line has come to be known as the Fujisawa point in recognition of the original work that suggested optimal outcomes with correction to this position. Anything beyond this point can be described as overcorrection and should be avoided because it can be associated with inferior cosmetic appearance and an unfavorable clinical functional outcome ( Fig. 23.1 ). Undercorrection, on the other hand, has also been discussed as problematic. However, a recent study demonstrated that, in those cases, a positive effect can still be achieved, based on the subsequent change in adductor moment following correction. It is yet to be determined if the long-term outcome is compromised by such undercorrection. Current consensus with regard to ligament and joint preservation procedures suggests not to correct into valgus, but opt for a more neutral limb alignment instead. In the varus knee, correction should have the achieved mechanical axis run through the lateral tibial spine. However, in the valgus knee, it is accepted that correction into a neutral position is optimal to avoid overloading of the medial compartment.

Strategy 2: Accurate Imaging, Templating, and Calculation of Correction

Proper preoperative imaging is essential to arrive at the correct diagnosis and enable accurate templating, and thus appropriate surgical management. ^, ^, ^, ^, ^, Standard imaging protocols include bilateral knee weight-bearing anteroposterior views in full extension, bilateral knee weight-bearing posteroanterior views in 45 degrees of flexion, and lateral knee and patella skyline views. Lateral joint line–centered views should be taken to measure tibial slope. Bilateral full-leg weight-bearing hip-to-ankle anteroposterior radiographs should be acquired for (computer-aided) templating and to evaluate for side differences in joint alignment. ^, ^, ^, Anatomical and mechanical axes of the lower extremities should be determined, and the site of the deformity should be assessed by defining the center of rotation and angulation as described by Paley. Here, a strong knowledge of the limits of normal (physiological) alignment is imperative to understand and adequately address pathology ( Fig. 23.2 ).

Coronal plane correction for HTO is calculated according to the technique proposed by Dugdale at the authors’ institution. This method essentially makes use of the planned mechanical axis and, through principles of trigonometry, creates a simple linear correction that can be translated into a distinct distance or an angle ( Fig. 23.3 ). Another method was described by Miniaci and uses lines projecting the angle of correction and resulting mechanical axis to determine a similar linear correction. ^,

In some instances, combined femoral and tibial deformity needs to be addressed. Here, a double-level osteotomy may be indicated to ensure that preexisting joint line obliquity is not altered excessively. In general, joint line obliquity of up to 10 degrees is tolerated in the short term, although long-term effects still remain to be investigated.

Planning techniques for DFO are adapted accordingly as described by bot Dugdale and Miniaci. In varus knees with lateral compartment osteoarthritis, the desired weight-bearing mechanical axis should run just medial to the medial tibial spine, whereas in valgus knees with fewer degenerative changes in the lateral compartment, it may be translated to the physiological position through the center of the knee. ^, ^, ^,

Inadvertent Alteration of Sagittal Plane Alignment

Sagittal alignment is assessed on a true lateral radiograph of the knee. Although it may not be the primary target for correction in most cases, it is essential that surgeons be conscious of evaluating tibial slope to avoid an inadvertent change during more common coronal plane correction. Medial opening-wedge HTO has been associated with increasing posterior tibial slopes. However, in our experience, this is often secondary to poor surgical technique and a lack of understanding of the three-dimensional geometry of the proximal tibia. Most recently, alteration of the tibial slope has also been used as an actual treatment option to address ligamentous deficiency and modulate contact pressures on the tibial surface, giving a hint to its powerful effects if performed without intention. Increasing posterior tibial slope will increase anteroposterior joint contact forces and reduce posterior tibial translation, which can be very helpful when addressing the posterior cruciate ligament–deficient knee. Decreasing the slope, on the other hand, will decrease anteroposterior joint contact forces and reduce anterior tibial translation, which therefore can be helpful in addressing the anterior cruciate ligament (ACL)–deficient knee. Because slopes greater than the physiological range have also been associated with ACL deficiency (>12 degrees), tibial slope–decreasing osteotomies may also be helpful in reducing graft forces in cases of ACL reconstruction revision. ^, Similarly, when performing combined HTO and ACL reconstruction, particular care must be taken not to inadvertently increase the tibial slope, as this might increase the risk of graft failure. ^,

Strategy 3: Maintaining or Altering Tibial Slope

Tibial slope is of great concern during tibial osteotomies such as medial opening wedge high tibial osteotomy (MOWHTO). Inadvertent increase of the tibial slope by 2 to 5 degrees during MOWHTO has been described in the literature. ^, To avoid this complication ( Fig. 23.4 ), the osteotomy should be opened twice as much at the posterior cortex as at the anterior cortex, hence creating a trapezoid-shaped osteotomy. The leg should be extended with the knee in a sagging position, and the wedge or lamina spreader should be placed as posterior as possible. The tibial slope may then be assessed with lateral fluoroscopy before applying the final fixation device.

Once in an appropriate position, a proximal HTO plate is inserted. Care must be taken with screw insertion because the obliquity of the medial proximal tibia can predispose to inadvertent intraarticular screw placement. Additionally, the plate should be placed as posteriorly as possible on the tibia to prevent loss of correction or cosmetic concerns, as well as mechanical irritation. ^,

Intraoperative Complications

The following procedures have specific complications associated with them. As such, each procedure will be dealt with in turn, providing associated complications and strategies to reduce risk.

Medial Opening Wedge High Tibial Osteotomy

Fowler described a technique for MOWHTO. The following intraoperative steps may be used in an attempt to mitigate the risk of complications ( Table 23.1 ):

1)

Skin incision: The procedure is carried out through a medial 5-cm longitudinal proximal tibial incision, 1 cm distal to the joint line centered in the sagittal plane between the anterior tibial tubercle and the posterior tibial border. Patients are regularly left with numbness in the distribution of the infrapatellar branch of the saphenous nerve as it is stretched or incised during the approach. An oblique incision might be used in an attempt to mitigate nerve injury, as has been described for hamstring tendon harvest ( Fig. 23.5 ).

• Fig. 23.5

Oblique incision as an approach to medial opening wedge high tibial osteotomy. This might help mitigate the risk for postoperative numbness following inadvertent incision or stretching of the infrapatellar branch of the saphenous nerve, as it follows its direction rather than crossing it.
2)

Posterior soft tissue protection: Dissection is brought down to the sartorial fascia, and the pes anserine tendons are identified. The sartorial fascia is released off the medial collateral ligament (MCL) in line with the upper border of the gracillis tendon, and a blunt retractor is placed along the posterior border of the tibia over to the proximal fibula to protect the popliteus muscle belly and the posterior neurovascular structures along with it. This will also allow for posterior visualization during the actual tibial osteotomy. Neurovascular injuries can be catastrophic, leaving the patient with life-threatening bleeding or other major neurologic symptoms such as a drop foot. These complications may require vascular repair and/or nerve reconstruction, or even amputation. Cases of popliteal vascular injury and tibial or peroneal nerve injury thankfully are rare; however, they exemplify the need for these kind of procedures to be performed by appropriately trained surgeons in centers where appropriate expertise is available if needed.
3)

Protection of patella tendon: Anteriorly, dissection is carried under the proximal aspect of the patella tendon insertion, and a small blunt retractor is used underneath, allowing for visualization of the tubercle insertion site during the osteotomy. Patella tendon injury has, however, not been reported as a major concern in the current literature.
4)

Location of lateral hinge: Using fluoroscopy, a K-wire is placed at the medial metaphyseal-diaphyseal junction of the proximal tibia and is inserted from medial to lateral to at least 2 cm below the joint line and 1 cm from the lateral cortex. Ensuring that the hinge placement is at least two times the distance from the joint line as from the lateral cortex will reduce the risk of fracture propagation to the articular surface of the lateral tibial plateau. Intraarticular tibial plateau fractures have been shown to occur in about 2.8% of cases. In these cases, it is important to achieve anatomic reduction and compression of the fracture with a laterally placed compression screw ( Fig. 23.6 ).

• Fig. 23.6

Lateral intraarticular tibial plateau fracture that propagated during medial opening wedge high tibial osteotomy. The fracture was reduced and fixed with a compression screw, while the osteotomy was still fixed with a conventional locking high tibial osteotomy plate.
5)

Creation of osteotomy: A small-diameter, thin oscillating saw blade is used to open up the medial cortex distal to the K-wire. This is followed by a combination of flexible and rigid osteotomes to complete the cut. Use of osteotomes to cut the posterior cortex will help reduce the risk of vascular injury. The osteotomy should stop approximately 1 cm from the lateral cortex. Meticulous use of the osteotomes and using fluoroscopy can prevent misdirection or violation of the lateral cortex.