Although correct bone resection recreates the proper alignment of the femur to the tibia, when performed alone, it will not have addressed the soft tissue imbalance. Bone resection does, however, establish the orientation of the prosthetic components with respect to the axes of the femur and tibia. Because of this, the surgeon is limited to orienting his distal femoral and proximal tibial cuts so that the resulting prosthetic joint will be appropriately aligned. Such proper alignment is independent of soft tissue balancing considerations and, rather, is dependent upon parameters of individual body build.

The authors have accepted the following as constituting proper alignment at total knee arthroplasty:

The prosthetic joint shall be centered on the mechanical axis of the lower extremity and shall be horizontal to the ground in anatomic two-legged stance (Fig. 11.1.1).

Anatomic two-legged stance is that position assumed by a subject standing with knees extended and both lower extremities adducted so that the feet approach the midline. This orientation of an individual lower extremity is also very close to the position assumed during mid stance phase of normal gait.

If a prosthetic joint is to be well aligned, then the orientation of the distal femoral cut to the shaft of the femur and the orientation of the proximal tibial cut to the shaft of the tibia are predetermined for a given patient. This fact can be appreciated by first considering a situation wherein the distal femoral and proximal tibial cuts are properly oriented and the knee prosthesis is properly aligned in anatomic two legged stance. If, instead, a slightly different distal femoral cut had been made, one which has a greater valgus angulation with respect to the shaft of the femur, then the center of the femoral head would come to lie lateral to a line coming up from the center of the ankle through the center of the knee (Fig. 11.1.2). In this instance, if a mechanical axis line were constructed from the center of the femoral head to the center of the ankle, the mid point of the knee would lie medial to that line.

The fact that the inclinations of the distal femoral and proximal tibial cuts are fixed and determined individually according to body build may be appreciated from an additional viewpoint. Assuming that deformity has been corrected and that the extremities have been properly "straightened," the lines connecting the centers of the femoral heads, each femoral head to each respective ankle, and last, the centers of the ankles, form a trapezoid whose size and shape is unique for the patient (Fig. 11.1.6). The construction of such a trapezoid with the subject positioned in anatomic stance determines the inclination of that patient’s mechanical axes with the vertical, usually 2.5—3°. Since the tibial shaft axis is coincident with the tibial segment of the mechanical axis, the orientation of the tibial cut with respect to the tibia itself must be the same as the orientation of the mechanical axis with a horizontal line.

David S. Hungerford, M.D., and Dennis W. Lennox, M.D.

Fixed valgus deformity is more likely to require special surgical techniques than are other deformities. There are several reasons for this. First, the principal lateral stabilizers of the knee are muscles: the popliteus, the tensor fascia lata and the biceps femoris. This means that deformity is more likely to become fixed at an early stage. Second, more severe valgus deformity or deformity of long standing is likely to be associated with attenuation of medial capsular stabilizers. Because the principal medial stabilizers are not attached to muscles, residual static medial instability is likely to create functional instability. For these reasons, fixed valgus deformity is one of the more difficult problems to be addressed at total knee arthroplasty.

Dynamic soft tissue stability of the lateral knee arises from four musculotendinous units: the iliotibial tract, the biceps femoris, the popliteus and the lateral head of the gastrocnemius. Additional stability is afforded by the posterolateral capsule-arcuate complex and the lateral collateral ligament. The anatomy of this area is comprehensively reviewed in Chapter 1. The predilection for valgus deformity to become fixed may reflect the observation that, of the six lateral stabilizers of the knee, four are musculotendinous units.

The lateral structures which may require release are depicted in Figure 11.2.4. In general the sequence of release would be: 1) iliotibial tract, 2) posterolateral capsule, 3) lateral collateral ligament, 4) popliteus tendon, 5) biceps femoris tendon, and 6) lateral head of gastrocnemius. This sequence is proposed only as a basic plan to guide soft tissue release. The structures released early in the sequence are those which are most commonly responsible for deformity and which, on release or lengthening, are most likely to allow correction. The minimum amount is released which will allow correction of the deformity.

Just as each total knee arthroplasty is somewhat different, so too may the elements contributing to valgus deformity vary from individual to individual. Thus, preoperative and intraoperative palpation to determine which structures are responsible for lateral tightness should be utilized to guide soft tissue release rather than to adhere rigidly to a sequence of releases predetermined without regard to the particular knee under consideration. There is no substitute for intelligent intraoperative decision making.

A Z-plasty lengthening of lateral stabilizers is recommended over simple transection since some stability is afforded by repair. In the case of the musculotendinous units which afford dynamic stability, a lengthening procedure with repair seems preferable to tenotomy, particularly in the case of the strong iliotibial band which is a primary dynamic stabilizer of the lateral side of the joint.

TECHNIQUE OF LATERAL SOFT TISSUE RELEASE

Minimal soft tissue release laterally includes elevation of soft tissue from the lateral tibial plateau. If required, a next step will almost always include a Z-plasty with lengthening and subsequent repair of the iliotibial tract. This is performed near the insertion of the iliotibial tract without an additional incision. The iliotibial tract is palpated with the leg in full extension and the extensor mechanism everted to the lateral side. The anterior border of the tract is separated from the lateral retinaculum with which it blends. This accomplishes a lateral patellar release at the same time. Both the medial and lateral aspects of the iliotibial tract are then carefully isolated, and under direct vision the Z-plasty lengthening is performed. Correction should be tested by reinserting the spacertensor jig IV and extending the leg before proceeding to additional releases.

If release of the iliotibial tract is insufficient to allow correct limb alignment, then other structures to be released or lengthened in sequence include the posterolateral capsule, popliteus tendon, lateral collateral ligament, biceps femoris tendon and lateral head of the gastrocnemius muscle. To diminish the risk of damage to the peroneal nerve by excessive tension, a supplementary posterolateral incision is recommended when the lateral head of the gastrocnemius muscle and the biceps femoris tendon require release and Z-plasty. Decompression of the peroneal nerve should be performed as needed to avoid excessive tension. Proximal fibulectomy is one method to provide decompression of the peroneal nerve in severe valgus deformity correction but this is only rarely indicated.

SURGICAL MANAGEMENT OF TYPE II VALGUS DEFORMITY

There are two possible ways to deal with this severe form of valgus deformity to achieve both correction of deformity and stability. In the first case lateral release, sufficient to correct the deformity, is performed prior to making the proximal tibial cut. Although this will align the limb, the knee will not be stable medially. To produce stability, a thick tibial plateau will have to be inserted to compensate for medial laxity. This, however, requires additional lateral release and results in lengthening the leg through the knee. Simply correcting the deformity puts the peroneal nerve at risk. Lengthening the leg through the knee potentiates that risk. For extreme cases of medial instability, such an approach is virtually impossible. The case depicted in Figure 11.2.5 would require 15 mm of prosthesis just to take up medial soft tissue slack, in addition to any bone resected to obtain a flat proximal tibial cut. Even for less severe cases of Type II deformity, the insertion of an excessively thick tibial component separates the femoral and tibial attachments of the posterior cruciate ligament, causing it to be prematurely and excessively tight in flexion.

For these reasons, we prefer to produce stability in Type II deformity by medial soft tissue advancement. For moderate Type II deformity a limited lateral release, usually restricted to a Z-plasty lengthening of the iliotibial tract, is performed to allow alignment of the lower extremity prior to cutting the proximal tibia. The medial structures are advanced to produce stability after the prosthesis is implanted (see technique below).

For more severe forms of Type II deformity with extensive lateral contracture, the magnitude of the lateral release required can be diminished by proceeding first with a modest femoral shortening. Four millimeters of additional femoral shortening can be easily and quickly carried out and produces a significant decompressive effect on the lateral side. If one is already committed to a medial advancement, the additional medial instability which this additional femoral resection will produce is of no consequence. If it would not otherwise be necessary to effect a medial advancement, femoral shortening should not be employed. Thus, femoral shortening is contraindicated in Type I valgus deformity. If when the IA and IB jigs are in place in proper alignment, it can be seen that no bone will be removed from the lateral side, a few millimeters of the distal surface of the medial condyle can be removed with an oscillating saw. The IA and IB jigs are then repositioned and a femoral shortening will be automatically effected. If the need for femoral shortening is seen only after the spacer-tensor jig shows the magnitude and type of deformity, the following special technique is carried out.

If needed, the distal femur can safely be removed to the level of the collateral ligaments. The distal femoral cutting jig, IA, is reinserted into the central anchoring hole, and a 3/16" drill pin is positioned laterally across the distal femur and acts as a spacer between the bone and jig (Fig. 11.2.6). Next, the distal femoral cutting jig, IB, is inserted into the IA jig and fixed with two 1/8" drill pins. Varus-valgus and flexion-extension alignment are then rechecked with the alignment guide. The assembled jigs IA and IB leads to the removal of 9 mm of distal femur when jig IA is flush against the distal femur. Therefore, by using the 3/16" drill pin (5 mm) to hold jig IA away from the initial cut surface, only an additional 4 mm of distal femur will be removed. A thicker interposing spacer will lead to a correspondingly thinner additional resection and vice versa. Assuming that, after this additional resection, full extension and proper tibial axial alignment are possible, the standard procedure for fixing in place the transverse tibial cutting jig V is followed. After additional femoral resection, it will be necessary to reposition jig III and recut the anterior femur to accommodate the femoral trial prosthesis.

Tibial component thickness is then selected, based upon that size which provides lateral stability. Reattachment of the capsular-ligamentous flap is performed only after the proper components are permanently seated. With the knee just short of full extension and the components held reduced, the medial flap is advanced distally to provide medial stability and is stapled in place (Fig. 11.2.10). The staples should fix at least the end of the superficial medial collateral ligament and any other substantially thicker portions of the flap. The pes group is then reapproximated and sutured in place.

Postoperative management differs from the usual protocol in that a knee immobilizer is worn at all times when ambulating. The immobilizer is removed for supervised range of motion exercises. Overall management of the patient’s activity must be determined by the surgeon, who must consider the soft tissue quality, bone and ligament fixation and the patient’s ability to follow instructions. Consideration may be given to postoperative bracing, although this is a rare requirement.

A total knee replacement was performed utilizing the PCA components and the Universal Total Knee Instruments. To bring the knee into correct alignment, femoral shortening of 3 mm and release of the iliotibial tract were necessary. The medial collateral ligament and medial capsule were advanced and fixed with staples. She required one manipulation postoperatively, but otherwise her course was uncomplicated. Active and active-assisted range of motion exercises were started 4 days after surgery, but she was protected with a knee immobilizer during ambulation for 6 weeks. Follow-up at 23 months showed a well-aligned knee with stable range of motion from 0° to 95°, unlimited walking tolerance without external support, normal ascent and descent of stairs and, a 95-point rating on the 100-point scale (Fig. 11.2.12).

Case M.T. This 83-year-old white woman sustained a distal femoral fracture treated with a blade plate 10 years prior to admission, and subsequently suffered a tibial plateau fracture treated with traction 5 years prior to admission. Over the several months before presenting for this treatment, progressive deformity, pain and instability had rendered her nonambulatory (Fig. 11.2.13). Marked crepitation and patellar subluxation were noted on examination. Motion was limited to 10—80° of flexion. The valgus deformity of 35° was not passively correctible, and marked instability on the medial side was noted clinically and radiologically.

A total knee replacement was performed through a long medial patellar incision. The blade plate was transected utilizing the diamond wheel on the Midas Rex instrument, and the blade portion was removed. To achieve alignment, the iliotibial tract required Z-plasty as did the biceps femoris tendon, the lateral collateral ligament and the popliteus tendon. Because the complex tibial plateau fracture involved posterior displacement of that portion of the tibial plateau to which the posterior cruciate ligament is attached, Z-plasty lengthening of the posterior cruciate ligament was necessary to achieve adequate flexion. The medial capsule and superficial medial collateral ligament were advanced and fixed with staples. Osteotomy of the tibial tubercle was carried out in order to facilitate adequate exposure without a separate lateral incision. After the lateral structures had been lengthened by Z-plasty, but before the prosthesis was implanted, the peroneal nerve was mobilized to be certain that it was not under stretch with the correction of the deformity. Following this, the lateral structures were repaired through eversion of the extensor mechanism and flexion of the knee. All Z-plasty lengthenings of tendons were repaired with interrupted sutures and the tibial tubercle was reattached with oblique K-wires. Because of significant osteoporosis of the tibial tubercle, the repair was protected with a circumferential wire attached to a transverse bolt in the tibial crest (Fig. 11.2.14).

The patient was managed postoperatively in a splint and subsequently transferred to a continuous passive motion machine. She achieved 90° of flexion at the time of discharge, 4 weeks postoperatively and was independently ambulatory with a walker. At 8-month follow-up, she had 105° of stable flexion, full extension, normal alignment, no pain and a 5-block walking tolerance without support. The preoperative 100-point evaluation scale rating was 10 and the 8-month follow-up rating was 90.

Case K.T. A 42-year-old white man complained of progressively disabling right knee pain, valgus deformity and instability 14 years following a right lateral tibial plateau fracture and 4 years following a right lateral meniscectomy (Fig. 11.2.15). On examination marked patellofemoral crepitus was noted. The valgus deformity was not passively correctible, and there was marked medial instability. Roentgenograms demonstrated lateral tibial plateau depression with narrowing of the lateral joint space, osteophyte formation, subluxation of the patella and 18° of valgus deformity of the knee. A total knee replacement was carried out using the PCA total knee system and the Universal Total Knee Instruments. There was a large lateral plateau defect which required a bone graft using as bone stock the medial posterior femoral condyle which was resected in the course of making the femoral bone cuts. This was internally fixed with three pins. This bone graft provided a flat bed for implanting the resurfacing tibial component. It was therefore possible to implant all three components without methylmethacrylate. A Z-plasty lengthening of the iliotibial tract, popliteus tendon and lateral collateral ligament was necessary to appropriately align the lower extremity. The posterior cruciate ligament was preserved in function throughout the range of movement. The medial capsule and superficial medial collateral ligament were sharply reflected from the medial tibial metaphysis, advanced distally, stapled and reinforced with the pes anserinus tendons.

At 6-month follow-up, he had a well-aligned lower extremity (Fig. 11.2.16), stable range of movement from 0 to 105° of flexion, and no pain. Roentgenograms showed continuing intimate fit of the bone to the prosthetic components (Fig. 11.2.17).

Varus alignment of the leg as measured by the mechanical or anatomical axes may be caused by angulation through the femoral or tibial diaphysis (Fig. 11.3.4). Malunited fractures, or late results of skeletal dysplasias, rather than arthritis, are usually the etiologic causes in these cases. Roentgenograms extending from the hip to the ankle joint must always be obtained preoperatively lest such an angular diaphyseal deformity be inadvertently missed while one concentrated on knee pathology (Fig. 11.3.5).

Cartilage loss from the medial femoral-tibial joint space is the basic abnormality in almost every patient with an arthritic varus knee (Fig.11.3.4). This loss causes a diminution of the "spacer height" on the medial aspect of the joint. Varus deformity, due to cartilage loss alone, is generally completely correctible, that is, completely mobile. At surgery, merely restoring the joint height by an implant of sufficient thickness suffices to correct the deformity (Fig. 11.3.6).

Theoretically, if only the medial femoral-tibial cartilage were lost, (Fig. 11.3.7) unicompartmental replacement would be an effective surgical procedure (Fig. 11.3.8). Unfortunately, results for such medial replacement vary widely. Marmor (16) noted excellent results in only 33 of 56 patients (50%), and poor results in over 21%. He still felt, however, that the procedure was a valuable one for general use. It is of interest to note that in his published cases the x-rays revealed that the preoperative varus deformity was not corrected completely at the time of surgery. Mallory and Dolibois (14) stated that they corrected the varus deformity using either the Marmor or polycentric prostheses, and that over 90% of their patients had excellent or good results. Similar, optimistic results were reported by Scott and Santore (18). Englebrecht et al. (3), however, noted a 22% failure rate and Insall and Walker (6) a 26% failure rate. In our series (11), there was a 35% failure rate, the causes of which were manifold: adverse effects of wear particles on the lateral, unreplaced compartment, patellofemoral symptoms, recurrence of the deformity, inadequate initial correction or overcorrection of the deformity. Cartier and Villers (1) have attempted to overcome the alignment problems through a series of preoperative roentgenographic measurements (Fig. 11.3.9) which are then used as guides at surgery to determine implant thickness and placement. Technetium-99 bone scans may be used in a manner analogous to Coventry’s (2) use in tibial osteotomies to ascertain the condition of the lateral tibiofemoral compartment (Fig. 11.3.10). With these types of modifications in technique, unicompartmental replacement may again emerge as a valid procedure. It may especially be useful in the patient with traumatic arthritis due to a previous tibial plateau fracture, or the patient with osteonecrosis of the medial femoral condyle.

BONE LOSS

Bone loss from the medial femoral condyle or the medial tibial plateau can certainly cause varus deformity in the arthritic knee (Fig. 11.3.11). This bone loss results from overload of the subchondral bony areas. With any degree of varus deformity, there is a medial displacement of the force resultant during the stance phase of gait (Fig. 11.3.12) (15). The response is a thickening and buildup of bony trabeculae in the subchondral area as predicted by Wolff (19) and Pauwels (17). As this overload increases, this ability to form new bone is overshadowed by the accumulation of microfractures, and eventually there is bony collapse.

Correction of bone loss on the tibial side is correctible in at least three ways (13):

1. Make the tibial resection cut at a lower level than normal (Fig. 11.3.15). This method is less applicable when such resection goes well below the tubercle of Gerdy with its iliotibial band insertion. The surgeon must recognize that such resection will cause lateral laxity especially as the knee is brought to full extension.

2. Make the tibial resection cut at the normal level (just below the joint surface) and fill in the resultant defect medially with acrylic cement (Fig. 11.3.16). This method is applicable for smaller degrees of bony loss and works well when the cement remains contained within a circumferential bony bed. When, however, there has been loss of bone extending out to and including the medial cortex, the cement may be unsupported. The use of mesh or supporting screws, although suggested by some surgeons, still places the cement in an unsupported position. In these cases, the third method is applicable.

3. Make the tibial resection at the normal level and bone graft the medial defect (Fig. 11.3.17A). This method is applicable to larger degrees of bone loss when the two previous methods are not feasible. A convenient source of autogenous bone is the posterior aspect of the femoral condyles. Any remaining cartilage is removed from the condylar fragment, and the bone is affixed to the depressed tibial plateau with two counter-sunk cancellous bone screws (Fig. 11.3.17B). The screws are inserted and angled anteriorly and laterally into the tibia. The newly formed plateau is then trimmed to the level of the previously resected lateral tibial plateau, and a standard or appropriate thickness tibial plateau component is used (Fig. 11.3.17C). This method has been used for over 2 years and in 14 cases of severe varus deformity with marked bone loss (Fig. 1 1.3.18A—C). We have not noted any increased settling of the tibial implant nor any increase in radiolucency about the component as compared with a similar group in which bone grafts were not used. In this group of patients, the limb is protected from weight bearing for approximately 12 weeks awaiting incorporation of the bone graft.

The third anatomic component of varus knee deformity in the arthritic patient is soft tissue contracture on the medial side of the knee (12). This contracture is adaptive, following and perpetuating any varus deformity from either cartilage loss or bony loss. The media! structures, including the deep capsular ligament, the pes tendons, the superficial capsular ligament, and the posteromedial capsule, can all become contracted (Fig. 11.3.19). This contracture is accentuated if there are any medial tibial plateau osteophytes lifting up and tenting the medial capsular ligamentous complex.

Treatment for soft tissue contracture consists first of removing all medial osteophytes from both the tibial plateau and the femoral condyle. Next, the entire medial capsule and deep capsular ligament are elevated as a half sleeve from their attachment to the proximal tibia. The dissection should progress around the tibia posteriorly as far as necessary to release the contracture, separating all the structures inserting onto the metaphysis. For more severe contracture, it may be necessary to elevate the insertion of the superficial collateral ligament and to cross-cut or elevate the attachment of the capsular sleeve and pes tendons distally, allowing the entire medial sleeve to recess proximally (Fig. 11.3.20). In these cases, resection of the posterior cruciate ligament is frequently required for full correction of the deformity. The capsular sleeve may be reattached to metaphyseal bone by staples or it may be allowed to heal without specific fixation in its new proximal position (Fig. 11.3.21). This author has not used fixation in his series and has observed no specific problems while others advocate reattachment of the soft tissue sleeve (5). These patients are routinely kept in a knee splint for approximately 3 weeks to allow this healing to occur.

1. Resection of tibial plateau and femoral condylar marginal osteophytes.

2. Release of the medial capsular sleeve and, if necessary, proximal recession of the sleeve.

3. Correction of bone loss by one of the three methods described above.

4. Correction for cartilage loss by varying the height of the tibial implant used.

An additional technique for the management of severe varus deformity has been developed by Krackow (7) and employed by Krackow and Kenna (10). This approach involves tightening the soft tissue sleeve on the lateral side of the knee. It is emphasized that most patients with even moderate varus deformity will not require either the bone grafting technique or this lateral advancement. Most patients will tolerate a small to moderate amount of lateral laxity after total knee arthroplasty as long as good postoperative alignment has been achieved. However, with the very severe varus cases, these more extreme methods will be appropriate.

The lateral soft tissue advancement is particularly applicable in the following circumstances:

1. When, after medial soft tissue release and cementing of components, unacceptable lateral laxity exists.

2. When a situation analogous to Type II valgus deformity exists. That is, severe, longstanding varus deformity can create attenuation of the lateral soft structures to such a degree that unrealistic medial soft tissue release would be necessary to achieve ligamentous balance. In these cases, lateral advancement may be considered preferable to medial release.

3. When medial bone grafting seems undesirable either because the bone stock is of questionable quality, or the patient’s ability to comply with protracted partial weight bearing is uncertain.

A straight incision, slightly posterolateral along the posterior edge of the fibular head, is made from 1 ½" above the joint line to 2" distal to the tip of the fibular head (Fig. 11.3.22). The peroneal nerve is identified and mobilized posterolaterally dividing the fascial roof created by the peroneus longus muscle where the peroneal nerve crosses the neck of the fibula. Subperiosteal dissection completely around the distal aspect of the fibular neck is performed.

Before osteotomizing the fibula, an appropriately sized hole is drilled from the tip of the fibula, in an intramedullary direction into the proximal fibular shaft (Fig. 11.3.23). This hole is tapped to receive an ASIF 6.5 mm cancellous screw, an ASIF 4.5 mm malleolar screw or a Vitallium lag screw, whichever the surgeon deems most appropriate according to the size of the fibula and the equipment available. It is important that this fixation hole be predrilled to assure accurate positioning of the fibular head after a segment of fibular neck is removed.

An oscillating saw is used to osteotomize the fibula approximately ¾" to 1" distal to the tip of the fibula (Fig. 11.3.24). The osteotomy is made perpendicular to the fibular shaft axis. The resulting proximal fibular piece is grasped with a clamp and carefully dissected free from all capsular and fascial attachments to the lateral surface of the tibia, being careful to preserve the attachment of the biceps femoris tendon and the lateral collateral ligament to this piece of fibula. It is necessary that complete release from the tibia be achieved so that traction on the fibular head is restrained by the femoral attachment of the lateral collateral ligament. Otherwise adequate distal advancement of the lateral ligament will not be possible.

After final implantation of the femoral and tibial components, the knee is held in reduced position at approximately 10-20 degress of flexion. Gentle traction is placed on the fibular head which is brought alongside the remaining fibular shaft (Fig. 11.3.25). The amount of overlapping bone is marked and removed from the fibular shaft with an oscillating saw. Last, the knee is flexed, the tibia externally rotated, and the fibular head fixed with an intramedullary lag screw (Figs. 11.3.26 and 11.3.27). After wound closure the knee is protected in a splint unless a continuous passive motion device is employed. Range of motion, both active and gentle assisted passive motion, is begun in physical therapy at the standard time. Weight bearing during gait is performed for 6 weeks with a knee immobilizer in place, otherwise, postoperative management is identical to other cases of total knee arthroplasty.

Whether varus deformity is best managed by simple soft tissue release with osteophyte removal, major medical ligamentous revision, medial bone grafting, or lateral ligament advancement will depend upon many factors dependent upon the particular case at hand.

The one method that should not be used in correcting a varus deformity is that in which the resection plane of the proximal tibia is angulated. With such an approach, one or both of the following will occur. The prosthetic joint line will not be parallel to the floor in normal stance and/or residual varus deformity will be present. Asymmetrical loading will occur and premature loosening and increased cold flow can be expected. Protocols which suggest or require such resection and which do not suggest correction of soft tissue contractures when present should be viewed with great skepticism.

4. Fixed Flexion Contracture

Kenneth A. Krackow, M.D.

Before addressing the surgical techniques and the pre- and postoperative regimens, the basic principles which lead to problems for the flexion contracture cases will be outlined. From the introduction to this chapter and the previous sections it should be clear that fixed deformity implies relative tightness of soft tissue structures at the concave side of the deformity, which, in the case of flexion contracture, is the posterior aspect of the knee. Certainly, the knee can always be brought into full extension by resecting a sufficient amount of bone from the distal femur and proximal tibia (Fig. 11.4.1). It would appear, initially, that this approach to the problem with treating fixed flexion contracture by generous bone resection as postoperative rehabilitation, and attention to the potential quadriceps lag would be all that were necessary.

The knee is, in this case, the convex side of the deformity; and the convex side of the deformity possesses a relative surplus of the soft tissue sleeve. One might predict in this line of reasoning, that with the quadriceps being a dynamic mechanism, there would not be any great problem with treating fixed flexion contracture by generous bone resection as postoperative rehabilitation, and attention to the potential quadriceps lag would be all that were necessary.

To summarize, bone resection alone to correct fixed flexion contracture can lead to collateral instability on both the medial and lateral sides of the knee and, furthermore, this laxity will generally not be evident if collateral stability is tested in maximal extension. The problem of collateral laxity after bone resection for the flexion contracture case has implications for some cases of pure valgus or pure varus fixed deformity. While a primary soft tissue imbalance after bone resection is, obvious on the convex and concave aspects of the knee, the flexion contracture situation illustrates how a secondary, less obvious soft tissue imbalance occurs on the sites "adjacent" to the main deformity. For the flexion contracture case, the secondary imbalance is seen to be medial-lateral. If bone resection alone is used to correct alignment in pure valgus or varus cases, the same type of secondary imbalance produces soft tissue laxity in the anterior and posterior aspects of the knee. The primary imbalance is certainly medial or lateral, but this secondary imbalance does occur, i.e., quadriceps lag and recurvation. This is not merely a theoretical consideration but rather is a clinical fact worth appreciating.