Summary
The structure of the knee is complex,and its behavior can be unpredictable even in the most experienced hands.
However, the task of replacing the bone surfaces and balancing the ligaments can be made manageable by following a logical plan based on correct alignment throughout the arc of flexion and ligament release based on the function of each ligament. Optimal knee function requires correct varus-valgus alignment in all positions of flexion. This requires reliable anatomical landmarks for alignment both in flexion and extension. The long axes of the femur and tibia and the anterior-posterior axis of the femur are highly reliable and provide the guidelines for establishing stable alignment of the joint surfaces by plac- ing the tibia and patellar groove correctly in the median anterior-posterior plane through the entire arc of flexion.
Ligaments perform specific functions, and these func- tions differ in different positions of knee flexion. Know- ing their function and testing their tension provides the information necessary to release only the ligaments that are excessively tight, leaving those that are performing normally.Fractional release does not destabilize the knee, because other ligaments are retained, and because the peripheral attachments of the ligament to other soft-tis- sue structures such as the periosteum or synovial-capsu- lar tissue allow the released ligament to continue to func- tion. Ligament release does not cause instability. Failure to align the knee and release the tight ligaments,however, does cause instability, unreliable function, and excessive wear.With this knowledge, good instruments, and sound implants, the surgeon can align, balance, and stabilize the knee even when severe bone destruction and ligament contracture are present.
Introduction
Although the knee has been studied intensively for decades, it continues to confound investigators and to frustrate knee surgeons. Its intricate ligaments and com- plex joint surfaces interact in ways that defy description.
Nevertheless, the surgeon must repair and reconstruct
the damaged and arthritic knee so that its performance is near normal, and this requires decisions and adjust- ments made with reasonable accuracy under the pressure and time constraints of the operating room. This chapter simplifies the geometry and kinematics of the knee enough that the knee can be understood and managed ef- fectively. It establishes rules for resection and alignment that position the joint surfaces so that the ligaments can be balanced through the normal flexion arc; it illustrates stability tests that can be performed with ease, and it teaches safe guidelines for ligament release so that the ligament balancing can be performed quickly and effec- tively without destabilizing the knee.
⊡ Fig. 26-1.In the extended position the joint surface slopes medially approximately 3°. Tibial resection is perpendicular to the long axis of the tibia and mechanical axis of the lower extremity. The resection surface is 3° valgus to the articular surface. Femoral resection is perpendicular to the mechanical axis, and 5° valgus to the long axis of the femur. The resection surface is approximately 3° varus to the articular surface. These 3° ‘errors’
in the femoral and tibial surface resections compensate for one another, and result in surface resections that are parallel to one another and per- pendicular to the mechanical axis of the lower extremity. (Reprinted from [8] with permission from Springer-Verlag)
26 Assess and Release the Tight Ligament
L. A. Whiteside
Chapter 26 · Assess and Release the Tight Ligament – L. A. Whiteside
The long axis of the femur serves as the anatomical reference for alignment of the distal femoral cuts per- pendicular to the mechanical axis and AP plane. Cutting the distal femoral surfaces at a 5° valgus angle to the long axis of the femur places the joint surface perpendicular to the AP plane in the extended position [1]. Likewise, cut- ting the upper tibial surface perpendicular to the long axis of the tibia also places the tibial joint surface per- pendicular to the AP plane in extension (⊡Fig. 26-1).
The AP axis serves as the anatomical landmark for femoral resection in flexion [1, 3, 5, 6]. The AP axis can be constructed by marking the lateral edge of the PCL and the deepest part of the patellar groove. A line drawn be- tween these two points lies in the AP plane and passes through the center of the femoral head and down the long axis of the tibia (⊡Fig. 26-2).
The ligaments stabilizing the lateral side of the knee all have differing functions in the flexed and extended po- sitions [4, 6, 8, 9]. The lateral gastrocnemius tendon and capsule of the posterolateral corner, lateral collateral lig- ament (LCL), and popliteus tendon complex attach near the lateral femoral epicondyle and are stabilizers of the lateral side throughout the flexion arc. The lateral poste- rior capsule (PC) and iliotibial band attach far away from the epicondylar axis and are effective lateral stabilizers only in the extended position (⊡Fig. 26-3a, b).
On the medial side, the medial collateral ligament (MCL, anterior and posterior portions) is attached to
the epicondyle and is effective throughout the flexion arc [5, 7, 8, 10, 14]. The epicondylar attachment is broad enough that there is a difference in function of the an- terior and posterior portions of this ligament in flexion and extension. The medial posterior capsule attaches far from the epicondylar axis, and is tight only in exten- sion. The posterior cruciate ligament is attached slight- ly distal and posterior to the epicondylar axis, so it slackens in full extension and tightens in flexion (⊡Fig.
26-4a, b).
By using the three accessible anatomical axes, the femoral and tibial components can be positioned so that the knee is in correct varus-valgus alignment throughout the flexion arc.The ligaments then can be balanced by de- termining which ligaments are contracted based on their function in flexion and extension. Simply stated, liga- ments that attach to the femur on or near the epicondyles are effective both in flexion and extension, and those that attach distant from the epicondylar axis are effective either in flexion or extension, but not in both positions.
To extend this concept further, it can be stated that the portions of the ligament complexes that attach anterior- ly in the epicondylar areas stabilize primarily in flexion, and those that attach posteriorly in the epicondylar areas stabilize primarily in extension. Ligaments that attach far posteriorly on the tibia are most effective in extension, and those attaching anteriorly are primarily tensioned in flexion.
⊡ Fig. 26-2.With the knee flexed 90°, the joint surface resections are par- allel to the epicondylar axis and perpendicular to the AP axis of the femur.
The femoral neck is anteverted approximately 15° to the epicondylar axis.
When the knee is in functional position in flexion (walking up stairs or standing from a seated position), the positions of the femoral neck and epicondylar axis remain unchanged, and in the normal knee the tibia is vertical. (Reprinted from [8] with permission from Springer-Verlag)
⊡ Fig. 26-3a, b.a Lateral view of the knee showing the major lateral sta- tic stabilizing structures with the knee extended. The lateral gastrocne- mius tendon, lateral collateral ligament, lateral posterior capsule, popli- teus tendon, and iliotibial band all cross the joint perpendicular (or near- ly so) to its surface, and are capable of stabilizing the knee in the extended position. (Reprinted from [4] with permission from Lippincott Williams and Wilkins.) b Lateral view of the knee showing the major lateral static stabilizing structures with the knee flexed 90°. The lateral gastrocnemius tendon, posterolateral capsule, lateral collateral ligament, and popliteus tendon are the only effective lateral stabilizing structures with the knee flexed to this position. The iliotibial band is parallel to the joint surface, and the posterior capsule is slack. (Reprinted from [4] with permission from Lippincott Williams and Wilkins)
a b
Varus Knee
In the presence of articular surface deformity the joint surfaces themselves cannot be used as reference land- marks for measuring resection of the bone, so the anatomical references are especially important for correct varus-valgus alignment.The usual reliable landmarks for varus-valgus alignment of the femoral component in flex- ion include the posterior femoral condyles, the long axis of the tibia, and the tensed supporting ligaments. If the posterior femoral condyle wears and the tibial plateau collapses on the medial side of the knee, these normally reliable landmarks cannot be used.Instead,the AP axis of the femur is used as a reference line for the anterior and posterior femoral cuts and the long axis of the tibia is used for a reference line for the tibial cut, so that the joint surfaces are cut perpendicular to these two reference lines [3, 11] (⊡Fig. 26-5).
Once the joint surfaces have been resected correctly to establish normal varus and valgus alignment in flexion and extension, the trial components are inserted and lig-
or and posterior portions of the medial collateral liga- ment, the posterior capsule, and the posterior cruciate ligament has been at least partially established [5, 7, 8, 10, 14].Because the medial collateral ligament attaches to the medial femoral condyle through a band about 1.5 cm wide, and spreads across a much broader surface on the medial tibial flare as the anterior portion and posterior oblique portion of the medial collateral ligament, each cannot function identically in flexion and extension. In- stead the anterior portion tightens and the posterior oblique portion of the medial collateral ligament loosens as the knee flexes. When the knee fully extends the pos- terior oblique portion tightens and the anterior portion slackens. The posterior capsule slackens early in knee flexion, and tightens only in full extension. The posterior capsule normally has no effect on varus and valgus sta- bility in the flexed knee. The posterior cruciate ligament also is not a varus and valgus stabilizer in the normal
26
⊡Fig. 26-4a, b. a On the medial view, the medial collateral ligament (deep and superficial) is the primary medial stabilizer that is tight in ex- tension. The anterior fibers are slackened in full extension and the poste- rior fibers (posteromedial oblique ligament) are differentially tightened in extension because of their position in the medial femoral condyle. The lat- eral posterior capsule also is tight. Active medial stability is added by the medial hamstrings through the pes anserinus and semimembranosus.
(Reprinted with permission from Elsevier.) b Viewed from the medial side with the knee flexed, the medial stabilizing structures are the deep and superficial medial collateral ligament. The anterior fibers of the medial col- lateral ligament are taut and the posterior fibers are relatively lax because of their attachment more posteriorly on the femur. The posterior capsule is slack and is not effective in flexion. The semimembranosus and pes anserina are parallel with the joint and are incapable of supplying active stability in flexion. (Reprinted with permission from Elsevier)
⊡ Fig. 26-5.The anterior and posterior surfaces of the femur are resect- ed perpendicular to the anteroposterior axis and parallel to the epi- condylar axis. Similar to the long axis of the femur, the anteroposterior axis is used as a reliable reference axis to align these cuts. This axis is identified by marking the lateral edge of the posterior cruciate ligament and the deepest part of the patellar groove. The articular surfaces are resected per- pendicular to the anteroposterior axis and parallel to the epicondylar axis.
In most cases of varus knee the posterior femoral condyles maintain their normal 3° medial down-slope, and can be used for alignment of the femoral component in flexion. In this case, a 3° external rotational guide would be used to engage the posterior femoral condyles to place the an- terior and posterior femoral surfaces in neutral alignment. The long axis of the tibia is used as a reference for the upper tibial resection. This surface is resected perpendicular to the tibial long axis when viewed from the front, and with a 4°-7° posterior slope when viewed from the side. (Reprint- ed from [14] with permission from Lippincott Williams and Wilkins)
a b
Chapter 26 · Assess and Release the Tight Ligament – L. A. Whiteside
knee because of its distance from the medial and lateral condylar surfaces.
With this information the medial ligament structures of the knee can be released individually according to the
position in which excessive tightness is found: release of the anterior portion of the medial collateral ligament to correct inappropriate medial ligament tension in flexion (⊡ Fig. 26-6), release of the posterior oblique portion of the medial collateral ligament (⊡Fig. 26-7) and posterior medial capsule to correct inappropriate medial ligament tension in extension, and release of the posterior cruciate ligament to correct excessive femoral roll-back in flexion.
The posterior cruciate ligament is an important sec- ondary varus and valgus stabilizer in flexion and, in the absence of the medial collateral ligament, also is likely to function as an important medial stabilizing structure in extension.
Tight PCL
Because the PCL is a medial structure, it often is con- tracted in the varus knee and stretched in the valgus knee.
The tight PCL causes excessive roll-back of the femur [2].
When palpated with the knee in flexion, it feels extreme- ly tight.A simple and effective means of releasing the PCL is to remove the polyethylene trial component and elevate the bone attachment of the PCL directly from the tibia [8]
(⊡Fig. 26-8a, b).
⊡ Fig. 26-6.The taut anterior fibers are released subperiosteally. These fibers attach fairly far distally (8-10 cm), and the osteotome is passed far enough to completely release the anterior fibers. The attachment of the pes anserinus and posterior oblique fibers of the medial collateral liga- ment are left intact. (Reprinted from [14] with permission from Lippincott Williams and Wilkins)
⊡ Fig. 26-8a, b.a The posterior cruciate ligament is released with a small segment of bone from its posterior tibial attachment. A quarter-inch os- teotome is used to make several small cuts around the posterior cortical margin, and then the bone piece is levered loose. (Reprinted with per- mission from Elsevier). b The bone piece slides proximally 0.5-1 cm, slack- ening the posterior cruciate ligament. The synovial membrane remains in- tact, and the ligament remains unfrayed by the release. (Reprinted with permission from Elsevier)
⊡ Fig. 26-7.In this case, only the posterior portion of the medial collat- eral ligament should be released first. A curved half-inch osteotome is used to elevate all but the anterior portion of the medial collateral liga- ment. The osteotome is directed approximately 45° downward and tapped gently to release the posteromedial oblique fibers from the tibia and from the tendon of the semimembranosus. (Reprinted from [14] with permission from Lippincott Williams and Wilkins)
a b
Correction of alignment and elimination of articular sur- face deformity now can be achieved with modern instru- ments and alignment devices even in the most difficult valgus knees. Using the anteroposterior axis of the distal femoral surface or the epicondylar axis of the femur vir- tually has eliminated the rotational alignment problem of the femoral component and has paved the way to a ratio- nal approach to ligament balancing in the valgus knee [11]. Using the central axis of the femur and tibia as refer- ence lines for valgus angle ensures highly reproducible alignment in the frontal plane [3, 11]. Using the distal sur- face of the medial femoral condyle as the point of refer- ence for distal femoral resection ensures that the distal surface of the femur will be in correct position relative to the medial ligaments and the patella (⊡ Fig. 26-9). This ensures that the patellar groove, intercondylar notch, and condylar surfaces all are positioned correctly in exten- sion.
For alignment in flexion either the anteroposterior axis or the epicondylar axis of the femur is used as anatomical reference for resection of the anterior sur-
faces of the femur (⊡ Fig. 26-10). The posterior femoral condyles are unreliable as references for femoral compo- nent alignment because of lateral femoral condylar defi- ciency. Correct resection of the femoral surfaces prior to ligament balancing produces a laterally conveying joint space in flexion [17].
With the surfaces in correct alignment, ligament bal- ancing requires a rational approach for correct balance in flexion and extension. Consideration of the effects of the functions of the lateral stabilizing structures throughout the arc of flexion offers a basis from which to formulate this approach [4, 6, 8, 9]. The lateral collateral ligament is regarded as a stabilizing structure both in flexion and ex- tension,and has rotational as well as valgus stabilizing ef- fects. The popliteus tendon complex also has passive varus stabilizing effects in flexion and extension,and also has a prominent role in external rotational stabilization of the tibia on the femur. These two structures would be appropriate to release for a knee that is excessively tight laterally both in flexion and extension [12].
The iliotibial band is aligned perpendicular to the joint surface when the knee is extended,and therefore can provide lateral knee stability when the knee is extended.
But when the knee is flexed to 90°, the IT band is parallel to the joint surface and cannot stabilize the knee to varus
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⊡ Fig. 26-9.The intramedullary alignment rod lies slightly medial to the center of the patellar groove, and the cutting guide is set at a 5° valgus an- gle. This will align the joint surface perpendicular to the mechanical axis of the femur (a), and parallel to the epicondylar axis (b). The cutting guide seats against the high (medial) side, which is the reference for resection of the joint surfaces. The thickness of the implant is resected distally from the medial side. In some cases resection of the thickness of the implant from the medial side results in minimal or no resection from the lateral side of the distal femur. Regardless of the lateral bone deficit, the medial surface should be used as the reference surface, and augmentation of the lateral surface should be done to make up for the deficit. (Reprinted with permission from Elsevier)
⊡ Fig. 26-10.The cutting guide for femoral resection is aligned so the surfaces are resected perpendicular to the AP axis of the femur (a) and par- allel with the epicondylar axis (b), resecting the thickness of the implant from the intact medial femoral condyle, and much less from the deficient lateral side. This places the joint surfaces in anatomical position to correct the valgus position in flexion, and places the patellar groove correctly with the mechanical axis of the lower extremity. The tibial surface is resected perpendicular to the long axis of the tibia. The lateral ligaments are still tight, and the tibia is held in a valgus malalignment by the ligament contractures. (Reprinted from [9] with permission from Lippincott Williams and Wilkins)
Chapter 26 · Assess and Release the Tight Ligament – L. A. Whiteside
stress. The lateral posterior capsular structures are tight only in full extension and are slack when the knee is flexed. Release of either the posterior capsule or the IT band would have a rational basis only for a knee that is tight laterally in extension. Release of either would have little effect on lateral knee stability in the flexed posi- tion.
Thus, after total knee arthroplasty, the knee that is tight laterally in flexion and extension will be almost completely corrected by release of the lateral collateral ligament and popliteus tendon. No other structures af- ford lateral stability in flexion, so release of these two structures is all that is needed to correct the effects of the lateral ligament contracture in flexion (⊡ Fig. 26-11a).
However, in extension the IT band and the lateral poste- rior capsule are effective lateral stabilizers, and may still need release (⊡Fig. 26-11b).Knees that start out with tight lateral structures in flexion and extension often will re- quire further work to correct lateral tightness in exten- sion after release of the popliteus tendon and lateral col- lateral ligament. Because the IT band is easily accessible, it is the next lateral stabilizing structure to be released if
the knee remains tight laterally in extension. If the knee remains tight laterally even after the IT band release,then the posterior capsule can be released to finish correcting lateral ligament tightness [12] (⊡Fig. 26-12).
Because knee stability in extension is absolutely nec- essary for good function, these two extension stabilizers (IT band and lateral posterior capsule) should be released only as a last resort. If they are released first, before later- al laxity is tested in flexion, and the lateral collateral ligament and popliteus tendon are released to achieve ligament balance in flexion, then nothing will remain to provide crucial extension stability.
For reasons probably related to differences in defor- mity of the lateral side of the knee, the knee sometimes is tight laterally only in extension after the trial implants have been inserted or tensioners applied. In these cases the lateral collateral ligament and the popliteus tendon should not be released, but only the IT band and the lat- eral posterior capsule should be released to achieve liga- ment balance. Uncommonly, valgus knees require all sta- tic lateral stability structures to be released to adequate- ly correct the deformity and ligament imbalance.In these cases the biceps femoris muscle, the gastrocnemius mus- cle, and the deep fascia provide support for the lateral side of the knee until capsular healing occurs.
Acknowledgements.The author thanks William C. An- drea, CMI, for his assistance with preparation of the illustrations, and Diane J. Morton, MS, for her assistance with preparation of the manuscript.
⊡ Fig. 26-11a, b. a Now that the lateral collateral ligament, popliteus ten- don, and posterolateral corner have been released, they retract partially, but remain attached to the surrounding capsule and dense overlying syn- ovial membrane, and so continue to function as lateral stabilizers. Release of the popliteus tendon, lateral collateral ligament, and rarely the pos- terolateral corner capsule always corrects lateral ligament tension in flex- ion because these are the only structures that stabilize the lateral side of the knee in flexion. The iliotibial band and posterior capsule remain as sta- bilizers in extension and may still apply deforming forces, but only in the extended knee. (Reprinted with permission from Elsevier.) b If the knee re- mains tight laterally in extension, the iliotibial band should be released. In this case the release is done just above the joint line, extrasynovially, so that the iliotibial band elongates but remains attached to the synovial membrane and can continue to support the lateral side of the knee in extension. The posterior cruciate ligament, posterior capsule, and biceps femoris remain as lateral stabilizers in extension. (Reprinted with permis- sion from Elsevier)
⊡ Fig. 26-12.In a few cases the knee remains tight laterally only in full extension after release of the iliotibial band. In these cases the lateral posterior capsule is the next structure to be released. The lateral posteri- or capsule is released by removing the polyethylene spacer and inserting the curved osteotome behind the knee against the femoral attachment of the posterior capsule, then gently tapping the end of the osteotome.
This release does not affect stability of the lateral side of the knee in flexion. (Reprinted with permission from Elsevier)
b a
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