Femoral Rotational Alignment Using the Tibial Shaft Axis in Total

CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 331, pp 47-55 0 1996 Lippincott-Raven Publishers

Femoral Rotational Alignment Using the Tibia1 Shaft Axis in

Total Knee Arthroplasty James B. Stiehl, MD; and Patrick M. Cherveny, MS

The capability of determining femoral component rotation by using a posterior femoral condyle resection made perpendicular to the longitudinal tibial shaft axis in posterior cruciate retaining total knee arthroplasty was eval- uated. From 100 consecutive cases, 54 used the femoral posterior condyle axis and 46 used an extramedullary alignment rod based on the tibial shaft axis. Seventy-two percent of total knee arthroplasties using the posterior condyle axis required lateral release versus 28% using the tibial shaft axis. Patellar fracture occurred in 7% using the posterior condyle axis versus none using the tibial shaft axis. Two patients had both techniques in opposite knees. Using computed tomography, the posterior condyle axis method gave a posterior condyle angle of 5' and 4' compared with the transepicondylar axis, whereas the tibial shaft axis technique measured 0' and lo. The posterior condyle resection using the tibial shaft axis restores the anatomic patellofemoral relationships, mini- mizing patellofemoral complications.

Numerous authors have cited the importance of proper rotational alignment of the femoral component in total knee arthropla~ty.*~4J7.24 Position of the patellar groove and flexion

From the Midwest Orthopedic Biomechanical Labora- tory, Columbia Hospital, Milwaukee, WI. Reprint requests to James B. Stiehl, MD, 2015 East Newport Avenue, #703, Milwaukee, WI 5321 1.

gap stability are determined by the femoral component rotation. Improper alignment can lead to abnormal articulation with the tibial component as well as altered patellofemoral tracking.*J4-*5-3O Rotational malalignment may lead to an increase in the risk of a total knee clinical failure from the complications associated with the patellofemoral joint. Patellar subluxation, dislocation, patellar clunk, ec- centric wear, and anterior knee pain have been described as complications of abnormal patellofemoral tracking .4- 1 1-34

With most modern total knee arthroplasty systems, for a given amount of proximal tibial resection, there is an appropriate amount of posterior condylar resection required to create a symmetric flexion gap.I1-37.40 In many instrumentation systems, femoral component rotation is set by equal resection of the posterior femoral condyles and 1 of the following methods for resection of the proximal tibia. The most common method is a perpendicular cut of the tibia about the mechanical axis of the tibia.30 For a knee with a varus joint line, this technique will result in ligamentous im- balance because more bone will be resected from the lateral side than from the medial side. Hungerford and Kenna'5 have described a second method in which the proximal tibia is resected at an angle of 93" in a varus direction to the mechanical axis of the tibia. This method will provide ligamentous

47

48 Stiehl and Cherveny Clinical Orthopaedics and Related Research

balance in flexion only for knees with a 3" varus joint line. Insa1117.'* proposed a method where resection was based on tensing the collateral ligaments of the flexion gap. In this method, resection of the proximal tibia is perpendicular to the mechanical axis of the tibia. Unequal posterior femoral condyle resection is undertaken to maintain ligamentous balance. Arima et a12 have described a technique that uses the anterior-posterior axis of the distal femur, defined as a line through the deepest point of the patellar groove and the center of the intercondylar notch. The anterior and posterior femoral cuts are made perpendicular to this axis. Thus, anatomic tensioning of the collateral ligaments in flexion is restored. The methods of Insa11~7J8 and Jiang and Insall* and Arima et aI2 result in a reconstruction in which the femoral component externally rotates on the femur resulting in better patellar mechanics, as the patellar groove is placed more later- ally.

The axis of the posterior femoral condyles has normally been used as the reference for neutral rotation of the fem~r.4.16~2OJo.45 This was thought to be a reasonable landmark because the goal of total knee arthroplasty is to reestablish alignment of the anatomic femoral condyles.21 However, recent biomechanical analyses have suggested that the transepicondylar axis and not the posterior condylar axis parallels the primary center of rotation of the knee joint. Nordin and Frankel33 demonstrated this relationship using instant centers of motion analysis. Muller3' has noted the importance of the transepicondylar axis as the origin of the collateral ligaments and consequently an important point on the Burmester curve in the the- ory of 4-bar linkage. Elias et a19 found a similar relationship, stating that the origin of the collateral ligaments and the cruciate ligaments are located in the center of circles created from the medial and lateral posterior condyles.

Bergher et a14 and Mantas et aP4 have drawn attention to the transepicondylar axis

as an important landmark for determining femoral component rotation. Bergher et a14 found that the angle between the posterior condylar surface and the surgical epicondylar axis, defined as the line connecting the lateral epicondylar prominence and medial sulcus of the medial epicondyle, was variable dependent on gender. They found a mean posterior condylar angle of 3.5" (k1.2") of internal rotation for males and a mean posterior condylar angle of 0.3" (k1.2") of internal rotation for females. Similarly, Mantas et a124 found a nearly constant relationship of 5" external rotation of the transepicondylar axis from the posterior condylar axis. The lateral epicondyle was closer to the joint line than the medial epicondyle in extension and flexion.

In a previous study from the authors' laboratory, measurements were made on 13 em- balmed anatomic specimens to determine the relationship of the transepicondylar axis to the longitudinal axis of the lower extremity in extension and flexion.40 The purpose of that study was to confirm whether the transepicondylar axis could be used to reliably determine posterior condyle resection in total knee arthroplasty. The anatomic study clearly defined a constant relationship of the transepicondylar axis to the transverse flexion axis of knee rotation and as a line perpendicular to the mechanical axis of the lower extremity. Most importantly, when the knee moves from extension to flexion, a perpendicular relationship is maintained from the transepicondylar axis to the lower extremity centered on the midline of the talus. The mean tibial angle comparing the transepicondylar axis to the mechanical axis was 0.4" varus in extension and 0.43" varus in flexion with no significant difference. It was also noted that the center of the knee, defined in the study as the lowest point of the intercondylar notch at the transepicondylar axis, was located virtually on the mechanical axis of the leg as was the center of the tibial eminence. The data for this study was nearly identical to the data of Yoshioka et al,45 comparing the transepi-

Number 331 October, 1996 Femoral Rotational Alianrnent 49

condylar axis to the mechanical axis, though they used the anterolateral origin of the posterior cruciate ligament as the knee center. A relationship of approximately 1 " varus angu- lation between the anatomic femoral and tibial axes compared with the mechanical axis is supported by Yoshioka et al,45 Moreland et a1,'O and Stiehl and Abbott.40 Similarly, Jiang and Insall20 and Oswald et a134 found a constant relationship between the mechanical axis and the anatomic femoral shaft axis of 5" to 6". The radiographic study of Moreland et a129 suggests that the anatomic femoral shaft axis and the mechanical axis have a 6" angle, but furthermore intersect in the supracondy- lar area closer to the transepicondylar axis than the joint line.

This study describes and verifies a technique for defining the distal femoral component rotational alignment based on the longitudinal tibial shaft axis and its relationship to the transepicondylar axis in total knee arthroplasty. From a clinical series that used ei- ther the posterior condylar axis or tibial shaft axis for femoral component alignment, the authors wanted to know if patellar complications and the need for lateral release could be reduced.

MATERIALS AND METHODS

One hundred consecutive primary total knee arthroplasties were performed by a single surgeon (JBS). The patient population consisted of 52 female (68 knees) and 25 male (32 knees) patients. Average age of the patients was 65.9 years. The preoperative diagnoses of the knees were osteoarthritis (88%), rheumatoid arthritis ( 1 0%), and avascular necrosis (2%).

In all 100 knees, intramedullary alignment instrumentation was used for femoral component orientation. To determine the distal femoral component rotational alignment, 2 different instrumentation techniques were used. The posterior condylar axis was used as the reference for posterior femoral cuts in the first 54 consccutive knees, and an extramedullary alignment rod was used i n the next 46 knees. Four standard knee prostheses (Whiteside Ortholoc, Wright Medical-

Dow Corning, Arlington, TN; Axiom, Orthomet, Inc, Minneapolis, MN; Genesis, Smith-Nephew- Richards, Memphis, TN; Lacey, Wright Medical - Dow Corning, Arlington, TN) were used in this study (Table 1).

All patients were observed by sequential phys- ical examinations and radiographic evaluations for a minimum of 3 years. Specific questions were asked regarding mechanical function and pain related to the patellofemoral joint. In partic- ular, the authors were interested in finding patellofemoral problems related to locking, catching, dislocation, subluxation, or patellar fracture. The need for lateral release obtained using the posterior condylar axis method and the tibial shaft axis method were compared by means of a chi square test with continuity correction (Yates' Correc- tion),l3 and the number of patellar complications were compared by means of Fisher's exact test.I3,?6

Surgical Technique After standard knee exposure, the medullary canal was entered at the midline of the femoral trochlea just anterior to the origin of the posterior cruciate ligament in the intercondylar notch using a drill bit appropriate for the desired knee system. Alternatively, the intramedullary rod was inserted at the location just posterior to the deepest point of the intercondylar groove. Using a total knee intramedullary femoral alignment system, the appropriate intramedullary rod was introduced into the medullary canal to the level of the isthmus to confirm unobstructed passage. At this point, the surgeon had the choice between the posterior condylar axis method or the tibial shaft axis method to determine femoral component rotational alignment.

Posterior Condylar Axis Method Each of the 4 standard knee prostheses used in this study had their own cutting guides that were used for the distal femoral resection. The appropriate distal femoral cutting guide was used to line up on the posterior condyles to determine the anterior-posterior distal femoral cuts. The flange of the rod was then introduced into the femur holding the rotation appropriately. Once the distal femoral cutting block was adequately seated, the distal femoral cuts were made using an oscillating saw. After this, the distal femoral cutting guide was removed and a second femoral cutting block

50 Stiehl and Cherveny Clinical Orthopaedics and Related Research

TABLE 1. Patient Characteristics for 2 Different Techniques for Femoral Component Rotational Orientation

Posterior Condylar Tibial Shaft Variable Axis Method Axis Method

Patients 54 46 Right total knee arthroplasty 25 26 Left total knee arthroplasty 29 20

Gender (%) Male 25.9 39.1 Female 74.1 60.9

Mean 66.6 65.1 Age (years)

Range 42-85 19-87 Preoperative diagnosis

Osteoarthritis 46 42 Rheumatoid arthritis 7 3 Avascular necrosis 1 1

Whiteside 46 27 Cemented 21 10 Cementless 9 6 Hybrid 16 11

Orthomet 4 19 Cemented 3 10 Cementless 0 0 Hybrid 1 9

Genesis 1 Cemented 0 Cementless 0 Hybrid 1

Lacey 1 Cemented 0 Cementless 0 Hybrid 1

Prosthetic types

-

-

-

-

-

-

-

-

was placed on the intramedullary rod. When the femoral block was appropriately seated, drill bits were used to attach the block to the distal femur. An oscillating saw was then used to make the anterior, posterior, and 2 chamfer cuts. The cutting block and intramedullary rod were then removed.

Tibial Shaft Axis Method For this method, a long extramedullary rod was designed so that it could be placed on the femoral intramedullary alignment rod with the knee in flexion. This extramedullary rod was used to determine the amount of external rotation required to balance the flexion gap based on the relation-

ship of a perpendicular tibia cut to the lower limb axis. After insertion of the appropriate intramedullary rod, the extramedullary alignment rod was attached to the femoral intramedullary rod and rotation of the rod in the transverse plane was determined. The extramedullary rod aligns distally to the center of the talar dome (Fig 1) . The femoral intramedullary alignment rod was then driven into position, engaging the fins to prevent rotation. In general, bone loss from the posterior condyles is negligible and the minimal bone loss from the tibia1 plateau can be disre- garded. If significant deformity and bone defi- ciency existed, a lamina spreader was used to

Number 331 October, 1996 Femoral Rotational Alignment 51

Fig 1. Transverse distal femoral computed to- mograms at the level of the transepicondylar axis of a patient who underwent bilateral total knee arthroplasty. The angle of the posterior condylar axis (PCA) measured in relation to the transepicondylar axis (TEA) was found to be 4" in the right (R) knee, in which equal resection was undertaken; and 0" in the left (L) knee, in which the extramedullary alignment rod was used.

tension the eroded joint space to correct the po- tential resection error. The appropriate anterior- posterior cutting block was applied and the posterior condyles were resected with an oscillating saw based on a plane perpendicular to the me-

chanical axis of the lower limb, after which were made the anterior, posterior, and chamfer cuts. The cutting block and intramedullary rod were removed and an oscillating saw was used to remove any remaining bone (Fig 2).

Lateral Release After the femoral cuts were made, attention was directed to the tibia. Tibia1 cuts were made according to the standard protocol for the given total knee system. The resultant gap must be of the same thickness as the prosthesis, with balanced tension in the medial and lateral collateral ligaments. Once all cuts were made, the knee components were placed into position according to their respective standard protocols. The knee was placed through a range of motion (ROM) test to examine patellar tracking of the knee system. For knees in which tracking was not optimal, where there was a tendency of the patellar implant to lose medial prosthetic contact with the no thumbs assessment, a lateral release was performed for the purpose of improving patellar tracking. The extent of the lateral release was dependent on the individual case. A release was performed first on the areas that felt tightest by palpation. The cap- sular and iliotibial band fibers were externally di- vided in a longitudinal direction, approximately 2 cm lateral to the patella. Care was taken to avoid the superior lateral circulation to the patella. In some cases, an adequate lateral release required interruption of the supralateral genicular vessels.

Fig 2A-B. (A) lntramedullary rod is placed in the distal femur while extramedullary rod alignment is used to determine distal femoral external rotation centering distally on the middle of the ankle joint with the Whiteside Ortholoc TKA instrumentation. (B) lntramedullary alignment of the Orthomet Ax- iom total knee arthroplasty instrumentation is used with the extramedullary alignment rod centering on the ankle joint.

Clinical Orthopaedics 52 Stiehl and Cherveny and Related Research

TABLE 2. Lateral Release Results in Patients Who Had Total Knee Arthroplasty Using the Posterior Condylar Axis Method or theTibial Shaft Axis Alignment Method

Number of Patients Alignment Method Lateral Release No Lateral Release

Posterior condyles 39 15 Tibial shaft 13 33

Postoperative Management All patients were treated with a protocol where continuous passive motion started approximately 24 hours after surgery as well as ROM and strengthening exercises. Patients with cemented implants were full weightbearing by the second postoperative day whereas patients with cementless implants maintained partial weightbearing at 50 to 75 pounds for 6 weeks. Discharge from the hospital required at least 70" passive flexion.

RESULTS

Thirty-nine of the 54 (72.2%) patients who underwent total knee arthroplasty using the posterior condylar axis method for determining femoral component rotation had a lateral release performed, whereas only 13 of the 46 (28.3%) patients who underwent total knee arthroplasty using the extramedullary alignment rod had a lateral release performed (Table 2). Results of the chi square test showed that the tibia1 shaft axis alignment method is associated with lower rates of lateral release (p c 0.001). Patellar fractures were found in 4 of the 54 (7.41%) knees us-

ing the posterior condylar axis method, whereas there were no patellar complications in the extramedullary alignment rod group (Table 3). Because of the small number of patellar fractures, there was no statistical difference between the 2 groups.

All the patellar fractures occurred in total knee replacements performed referencing the posterior condylar axis for posterior femoral resection. It is interesting to note that all these patellar fractures occurred in female patients who underwent bilateral cemented (Whiteside Ortholoc) total knee arthroplasties. All these cases had a lateral release performed and the contralateral knee replacements had satisfactory clinical results.

Two of the patients underwent bilateral total knee arthroplasties on separate occa- sions such that equal posterior resection was used on 1 knee and extramedullary rotational alignment was undertaken on the contralat- era1 knee.40 Transverse computed tomo- graphs of each knee were made at the level of the epicondyles and the angle of the prosthetic posterior condyles was measured in relation to the transepicondylar axis. For the

TABLE 3. Patellar Fractures in Patients Who Had Total Knee Arthroplasty Using the Posterior Condylar Axis Method or theTibial Shaft Axis Alignment Method

Number of Patients Alignment Method Patellar Fractures Satisfactory Results Posterior condyles Tibial shaft

4 0

50 46

Number 331 October. 1996 Femoral Rotational Alianment 53

knees performed with equal posterior resection, the posterior condyle-transepicondylar axis angle measured 5.0" and 4.0", respectively. For the knees performed with the extramedullary alignment rod, the posterior condyle-transepicondylar axis angle measured l" and O.O", respectively (Fig l).

DISCUSSION

It is well known that optimum femoral component rotational orientation is essential for flexion gap balance, patellofemoral tracking, and normal kinematic function of the knee in total knee arthroplasty. From a previous anatomic study investigating the various relationships of the transepicondylar axis, the authors found that the perpendicular relationship of the transepicondylar axis to the longitudinal axis of the lower extremity in 90" flexion allows the transepicondylar axis to be used for accurate posterior condylar resection.40 By performing a perpendicular proximal tibia1 resection, the posterior condylar resection is parallel to the transepicondylar axis. This relationship allows the flexion gap to be prepared such that the ligaments can be appropriately balanced. Thus, appropriate femoral rotation in the transverse plane can be determined from this landmark.

Yoshioka et a145 have identified significant interspecimen variability of the posterior condylar axis in comparison to the nearly constant relationship defined by the femoral shaft to hip center axis and the transepicondylar axis. Femoral dysplasia at the distal end of the femur is matched by a compensatory reverse deformity in the proximal tibia. Consequently, the posterior condylar axis has a less reliable relationship to the mechanical axis. Anatomic and biomechanical data point to the transepicondylar axis as an important mechanical landmark as opposed to the posterior condylar axis.l.2.4 Yoshioka et a145 suggested that in total knee arthroplasty, the femoral component should be placed along a longitudinal axis that is centered at the knee, at the attachment of the

posterior cruciate ligament. Although the epicondyles have been shown to be reliable anatomic landmarks, it is difficult to localize the peaks of the epicondyles precisely during surgery.* To eliminate the need for finding the epicondyle peaks intraoperatively, the authors have used a long, extramedullary rod that can be attached to the intramedullary rod femoral alignment guide to define the amount of external rotation required to balance the flexion gap. This concept is easily adapted to any standard total knee instrumentation.

Major patellar complications, such as patellar dislocation or fracture, have been re- ported in 1 % to 12% of recent total knee arthroplasty cases and continue to be 1 of the leading causes of revision total knee arthroplasty. 11.28.37 Other minor problems, includ- ing anterior knee pain and patellar clicking, will occur even more frequently. The exact mechanism of patellar problems can be variable, but most may be attributable to malalignment of the prosthetic components, soft tissue imbalances, excessive valgus alignment, altered joint line, and tilted patellar c~t.5,10.11,*8~35J7 If the lower extremity is aligned properly at the time of surgery, mild degrees of instability may be tolerated; however, if malalignment is created at the time of surgery, minor degrees of instability can lead to patellar subluxation. Improper position and rotational malalignment of the knee system components may impose shear forces on the interface, which may lead to loosening.16

Figgie et all1 examined 36 knees that had fracture of the patellar after total knee arthroplasty. Results indicated that alignment and the fit of a component were important in determining the severity of a fracture of the patella. Of 1 1 6 knees, 16 (14%) of the patients had minor complaints of patellar problems, and 14 (12%) had significant mechanical problems with the patella. Rota- tional malalignment was a primary abnor- mality in all 6 knees that had to undergo revision total knee arthroplasty. In the report of 119 knees by Scott et al,38 6 (5%) patients

54 Stiehl and Cherveny

who had undergone extensive lateral releases had postoperative patellar fractures. One ad- ditional patient, who did not have a lateral release performed, dislocated the patella postoperatively. Malkani et a123 have re- ported patellar complications after total knee arthroplasty of 21%, 4%, and 12% with implants that require sacrifice, substitution, and preservation of the posterior cruciate ligament, respectively.7.'h.'Y The authors' experience would similarly indicate lateral release and femoral internal rotation as risk factors for patellar fracture.

Another factor that may influence the in- cidence of patellar complications in total knee arthroplasty is that of prosthetic design. In this clinical study, 4 standard knee systems were used; however, the majority of knee systems used were the Whiteside Or- tholoc and the Orthomet Axiom. Both implants have a relatively stable patellofemoral articulation as a design feature. Patellar subluxation was not identified in any of the patients. All the patellar fractures occurred with the Whiteside implants performed with equal posterior condyle resection. However, there were no patellar fractures occurring with the Whiteside implants performed with the extramedullary alignment rod.

A method is described that allows the anatomic amount of femoral component rotation based on the lower limb anatomic axis. Thus, if femoral preparation is undertaken first, appropriate posterior condyle resection can be performed in a manner that will allow a balanced flexion gap if the sub- sequent proximal tibial cut is made perpendicular to the same axis. Patellar fracture and the need for lateral retinacular release were diminished when this technique was compared with the posterior condylar axis method in similar implants. References

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Femoral Rotational Alignment Using the Tibial Shaft Axis in Total