The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 89, Issue 11

Scientific Articles | November 01, 2007

Effects of Posterolateral Reconstructions on External Tibial Rotation and Forces in a Posterior Cruciate Ligament Graft

Keith L. Markolf, PhD¹; Benjamin R. Graves, MD¹; Susan M. Sigward, PhD¹; Steven R. Jackson¹; David R. McAllister, MD¹

¹ Biomechanics Research Section, Department of Orthopaedic Surgery, University of California at Los Angeles Rehabilitation Center, 1000 Veteran Avenue, Room 21-67, Los Angeles, CA 90095-1759. E-mail address for K.L. Markolf: kmarkolf@mednet.ucla.edu

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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from NFL Charities. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

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Investigation performed at the Biomechanics Research Section, Department of Orthopaedic Surgery, David Geffen School of Medicine at the University of California at Los Angeles, Los Angeles, California

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2007 Nov 01;89(11):2351-2358. doi: 10.2106/JBJS.F.01086

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Abstract

Background: In patients with a Grade-3 injury, reconstructions of the lateral collateral ligament, popliteus tendon, and popliteofibular ligament are commonly performed in conjunction with a reconstruction of the posterior cruciate ligament. The objectives of this study were (1) to compare the abilities of three types of posterolateral graft reconstruction to restrain external tibial rotation and alter forces in a posterior cruciate graft and (2) to compare tibial rotations and posterior cruciate graft forces associated with two levels of initial posterolateral graft tension.

Methods: Forces in the posterior cruciate ligament were recorded as the knee was extended from 120° to 0° and a 5-N-m external tibial torque was applied. The posterior cruciate ligament was reconstructed, and external tibial rotation and the forces in the posterior cruciate graft were recorded. These measurements were again recorded after sectioning of the posterolateral structures and after reconstruction of the lateral collateral ligament, alone as well as in combination with reconstruction of the popliteus tendon and in combination with reconstruction of the popliteofibular ligament.

Results: With the lateral collateral ligament intact, removal of the popliteus tendon from its femoral origin significantly increased external tibial rotation. Applying tension to a popliteus or popliteofibular graft internally rotated the tibia, with no significant difference between the rotations caused by the tensioning of the two grafts. Tibial rotation was significantly greater when graft tensioning had been performed with the tibia free to rotate than it was when the tensioning had been done with the tibia locked in neutral rotation. With an applied external tibial torque, a reconstruction of the lateral collateral ligament alone was not sufficient to reduce posterior cruciate graft forces to normal. The addition of a popliteus or popliteofibular reconstruction to the lateral collateral ligament reconstruction significantly reduced posterior cruciate graft forces to normal (or below normal) levels. The external rotations associated with these two combined reconstructions were equivalent and significantly less than that in the intact knee. Increasing tension in either the popliteus or the popliteofibular graft from 10 to 30 N significantly decreased external rotation.

Conclusions: The posterolateral grafts acted to resist applied external torque, thereby off-loading the posterior cruciate graft. Popliteus and popliteofibular grafts were more favorably aligned than a lateral collateral ligament graft to resist external rotation, and they had similar effects.

Clinical Relevance: Holding the tibia in neutral rotation when tensioning a popliteus or popliteofibular graft will help limit internal tibial rotation. The popliteus and popliteofibular graft tensioning protocols used in this study overly constrained external rotation and failed to produce optimal load-sharing with the posterior cruciate graft.

Figures in this Article

Injuries to the posterolateral structures of the knee are commonly found in association with a posterior cruciate ligament injury^1-3. Normally, ruptures of the lateral collateral ligament are easily recognized, and an anatomic graft reconstruction is straightforward. However, injuries to the popliteus tendon and popliteofibular ligament are often unappreciated⁴, and a number of posterolateral reconstruction techniques have been described in the literature^5-8. The popliteus has an origin on the lateral femoral condyle, and it passes through the lateral aspect of the capsule to a muscular insertion on the posterior surface of the tibia. The popliteus bypass reconstruction is typically done with a tendon graft, with an origin at the popliteus footprint on the lateral femoral condyle, that passes beneath the lateral collateral ligamentand joint capsuleand into a tunnel drilled approximately 1 cm beneath the lateral tibial plateau^9-11. The popliteofibular ligament has an attachment on the fibular head near the posterior styloid and a diffuse connection to the posterolateral complex; it has no direct attachment to the femur¹². One method of reconstructing the popliteofibular ligament involves use of a tendon graft that originates at the center of the popliteus footprint on the femur and passes through a tunnel drilled at the fibular styloid. This reconstruction has direct bone-to-bone attachments, unlike the native ligament that it is replacing^8,9.

Previous biomechanical studies with application of external tibial torque have shown that external tibial rotation and forces in the native posterior cruciate ligament (and in a posterior cruciate ligament graft) increase significantly when the posterolateral structures are cut^13-15. However, there have been relatively few biomechanical studies on external rotatory laxity after the reconstruction of the posterolateral structures in knees with an intact posterior cruciate ligament^10,16 and those in which the posterior cruciate ligament has been reconstructed^17,18. The objectives of this study were to measure changes in tibial rotation and forces in a posterior cruciate ligament graft resulting from applied external tibial torque after removal of the popliteus tendon, popliteofibular ligament, and lateral collateral ligament and to repeat the measurements after reconstruction of the lateral collateral ligament alone, the lateral collateral ligament and the popliteus tendon, and the lateral collateral and popliteofibular ligaments. The effects of varying tension in the posterolateral grafts and of locked compared with unlocked tibial rotation during graft tensioning were also investigated.

Materials and Methods

Materials and Methods | Results | Discussion | Acknowledgements | References

Fifteen fresh-frozen cadaveric knees were used for this study. The mean age of the donors at the time of death was 35.1 years (range, seventeen to sixty-five years); thirteen donors were male, and two were female. A coring cutter was used to mechanically isolate a cylinder of bone containing the femoral origin of the posterior cruciate ligament. The bone cylinder was attached to a custom-designed femoral load cell that recorded force in the ligament as the knee was extended from 120° to 0° and 5 N-m of external tibial torque was applied. A single-bundle tibial inlay reconstruction of the posterior cruciate ligament was performed on each specimen with use of an 11-mm-wide bone-patellar tendon-bone graft. The femoral end of the graft was passed through a 10-mm-diameter tunnel drilled into an acrylic replica of the bone cylinder at the center of the femoral footprint of the anterolateral bundle of the posterior cruciate ligament. The acrylic replica was connected to the end of the femoral load cell. The graft was tensioned to restore anteroposterior laxity at 200 N to within 1 mm of that in the intact knee at 90° of flexion. The popliteus muscle belly was partially removed during installation of the tibial inlay bone block. Details of the load-cell installation, graft placement, and graft tensioning can be found in a prior publication¹⁹.

Tibial rotation and the resultant force in the posterior cruciate ligament graft were recorded continuously over a 120° flexion range with application of 5 N-m of external torque as described previously²⁰. Testing was repeated with the popliteus tendon detached from its femoral origin, and then the popliteofibular ligament was cut at its attachmentto the fibular styloid. A 1 × 1-cm calcaneal bone block of an Achilles tendon graft was fixed into a square mortised recess near the femoral footprint of the popliteus tendon; the tissue was sized to fit within a 7-mm-diameter tunnel. This graft was used for both the popliteus and the popliteofibular reconstruction. When used for the popliteofibular reconstruction, the tendon entered a tunnel drilled into the styloid of the fibula (Fig. 1). A high-strength, low-stretch synthetic line (135-lb [61.2-kg] test Spectra Fiber; Izorline, Gardena, California), sutured into the free end of the graft tissue with use of a whip stitch, was passed through a split clamp attached to the tibia anterior to the fibula(Fig. 1). When used to reconstruct the popliteus tendon, the Achilles tendon passed into a 7-mm-diameter tibial tunnel 1 cm inferior to the lateral tibial plateau. The line attached to the free end of the graft was passed through a separate split clamp, which wasalso located on the anterior aspect of the tibia(Fig. 1). These particular reconstructions were selected for experimental study because they represented the most simple and direct reconstructions of normal posterolateral anatomy. Since the amount of tension applied to a posterolateral graft and the rotational position of the tibia at the time of graft tensioning vary in the literature^21-23, these variables were also selected for study.

The precise location of the femoral bone-block site for the popliteus and popliteofibular grafts was determined after performance of isometry measurements. This was done by measuring relative length changes between trial locations on the lateral femoral condyle and the distal graft tunnel sites. A suture (fixed at a trial site) was passed through each tunnel and through a split clamp. A dial caliper was used to measure the relative length change between the split clamp and a forceps attached to the suture at a fixed distance from the split clamp. An optimum femoral point for both grafts was selected on the basis of the minimum relative length change of the suture. The bone block was placed such that the leading edge of the graft tissue on it was centered over the optimum point. For the reconstruction of the lateral collateral ligament, the mean center of the 1 × 1-cm calcaneal bone block was located 2.4 mm anterior to the anatomic center of the femoral footprint of the lateral collateral ligament. For the popliteus and popliteofibular reconstructions (the same graft was used for both), the mean bone-block center was 2.7 mm proximal and 11 mm anterior to the center of the popliteus footprint. The mean relative length changes of in situ lateral collateral, popliteus, and popliteofibular grafts with these bone-block placements were <1.5 mm from 0° to 90° of flexion.

An external torque test was performed with the distal lines of the popliteus or popliteofibular graft unclamped and the lateral collateral ligament removed (simulating a Grade-3 posterolateral injury). This test was performed first with the femoral origin of the popliteus intact and then with the popliteus tendon detached from the femur. Next, the lateral collateral ligament was reconstructed with use of a second Achilles tendon graft. The bone block of this graft was fixed into a mortised recess centered over the femoral footprint of the lateral collateral ligament. The tissue was sized to fit within a 6-mm-diameter tunnel drilled at the fibular insertion of the lateral collateral ligament (Fig. 1). External torque tests were performed at two graft-tension levels (10 and 30 N) after reconstruction of the lateral collateral ligament alone, reconstruction of the lateral collateral ligament and the popliteus tendon, and reconstruction of the lateral collateral and popliteofibular ligaments. The tibia was locked during tensioning.

Prior to external torque testing, the knee was moved through a passive range of motion (with no tibial torque applied) to record the internal tibial rotations caused by tensioning of the popliteus and popliteofibular grafts. The grafts were tested in random order. Each reconstruction was tested both with the graft tensioned to 10 N and with it tensioned to 30 N at 30° of flexion with the tibia locked in neutral rotation and with the tibia free to rotate.

A repeated-measures analysis of variance with paired comparisons was used to analyze differences in mean tibial rotations and graft forces between test conditions. The test conditions included the tibial rotation status (free or locked) during graft tensioning, the posterolateral corner status (popliteus attached, popliteus detached, or lateral collateral ligament removed), and the reconstruction status (reconstruction of the lateral collateral ligament alone, reconstruction of the lateral collateral ligament and the popliteus tendon, and reconstruction of the lateral collateral and popliteofibular ligaments), and the amount of graft pretension (10 or 30 N). The level of significance was p < 0.05.

Results

Materials and Methods | Results | Discussion | Acknowledgements | References

With the lateral collateral ligament and the femoral origin of the popliteus intact, the mean external tibial rotations resulting from the applied external torque were 9.1° at 0° of flexion, 14.1° at 30° of flexion, and 10.3° at 120° of flexion (Fig. 2). Detachment of the popliteus tendon from the femur significantly increased the mean external rotation by 1.6° at 0° of flexion to 7.3° at 120° of flexion. The mean external tibial rotations after all posterolateral structures were removed (a Grade-3 injury, with the lateral collateral ligament cut and the popliteus tendon detached) reached a maximum of 29.6° (at 35° of flexion) and were significantly greater than those for the other test conditions at all flexion angles (Fig. 2).

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Fig. 1:: The combined reconstruction of the lateral collateral ligament (LCL) and the popliteus tendon (POP). The bone block of the lateral collateral ligament graft is fixed on the lateral femoral condyle at the center of the native footprint of the lateral collateral ligament. The distal end of the graft passes through a tunnel on the fibular head. Lines sutured to the end of the graft pass through a split clamp (fixed to the tibia) for graft tensioning and fixation. The bone block of the popliteus graft is fixed near the center of the popliteus footprint on the lateral femoral condyle and passes through a tunnel drilled into the fibular styloid. When used for a popliteus reconstruction, the same graft passes through a tunnel drilled 1 cm inferior to the lateral tibial plateau. PFL = popliteofibular ligament. (Reprinted, with permission, from: Markolf KL, Graves BR, Sigward SM, Jackson SR, McAllister DR. How well do anatomical reconstructions of the posterolateral corner restore varus stability to the posterior cruciate ligament-reconstructed knee? Am J Sports Med. 2007;35:1117-22.)

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Fig. 2: Mean curves of tibial rotation versus knee flexion angle produced by application of 5 N-m of external tibial torque in the fifteen knees, with (1) the popliteus (pop) insertion intact, (2) the popliteus tendon detached from the lateral femoral condyle, and (3) the lateral collateral ligament (lcl), popliteus tendon, and popliteofibular ligament removed (a Grade-3 injury). PCL = posterior cruciate ligament. Sample standard deviations are indicated by error bars. P < 0.05 indicates a significant difference between test conditions.

The mean forces in the posterior cruciate ligament graft (resulting from the applied external torque) with the lateral collateral ligament and the origin of the popliteus intact were significantly greater than the forces in the intact posterior cruciate ligament beyond 50° of flexion (Fig. 3). The mean forces with the popliteus tendon detached were significantly greater than those with the popliteus intact beyond 80°, and they were significantly greater than those for the intact posterior cruciate ligament beyond 55°. The mean forces with all posterolateral structures removed were significantly greater than those with the popliteus detached beyond 15° and significantly greater than those in the posterior cruciate ligament beyond 5°. The mean posterior cruciate ligament forces remained near zero up to approximately 45° of flexion, at which point they began to increase. The mean posterior cruciate graft forces with all posterolateral structures removed were 119 ± 32 N at 45°, and they increased to a maximum of 197 ± 35 N at 110° (Fig. 3).

With an applied external tibial torque, the mean external rotations with a lateral collateral ligament graft were not significantly different from those with all posterolateral structures intact beyond 25° of flexion, and they were approximately 3.5° greater between 0° and 25° of flexion (Fig. 4). The mean rotations with 10 N of tension on the lateral collateral ligament graft were not significantly different from those with 30 N of tension. The mean rotations with the popliteus and popliteofibular grafts were significantly less than those with all posterolateral structures intact, with one exception (the popliteus graft at 0°) (Fig. 4). The mean rotations with both grafts were approximately 2° greater with 10 N of graft tension than they were with 30 N. The mean rotations with the popliteus and popliteofibular grafts were not significantly different from each other at either tension level.

With the tibia free to rotate, applying 30 N of tension to a popliteus or popliteofibular graft rotated the tibia internally to 5.5° at 0° of flexion and to 15.6° at 120° of flexion. There was significantly less mean internal rotation when the tibia was locked during tensioning (1.8° to 9.8°, respectively) (Fig. 5). For these tests, the lateral collateral ligament was intact and the knee was passively flexed through a 120° range of motion with no external tibial torque applied. The mean rotation with the popliteus graft did not differ significantly from that with the popliteofibular graft at either pretension condition (Fig. 5).

The mean forces in the posterior cruciate graft with a lateral collateral ligament reconstruction alone were significantly greater than those in the posterior cruciate ligament beyond 80° of flexion (Fig. 6). The mean posterior cruciate graft forces with reconstruction of the lateral collateral ligament and the popliteus tendon were not significantly different from the mean posterior cruciate ligament forces (Fig. 6). The mean posterior cruciate graft forces with reconstruction of the lateral collateral and popliteofibular ligaments were significantly less than the posterior cruciate ligament forces beyond 70° of flexion. The level of graft tension did not significantly affect the mean posterior cruciate graft forces associated with any reconstruction (Fig. 6).

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Fig. 3: Mean curves of resultant force versus knee flexion angle produced by application of 5 N-m of external tibial torque (with the lateral collateral ligament [lcl] intact) in the fifteen knees, with the posterior cruciate ligament (pcl) intact and with a posterior cruciate ligament graft and (1) the popliteus (pop) insertion intact, (2) the popliteus tendon detached from the lateral femoral condyle, and (3) the lateral collateral ligament, popliteus tendon, and popliteofibular ligament removed (a Grade-3 injury). Sample standard deviations are indicated by error bars. ns = no significant difference between test conditions at the indicated degrees of flexion.

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Fig. 4: Mean curves of tibial rotation versus knee flexion angle produced by application of 5 N-m of external tibial torque in the fifteen knees, with (1) all posterolateral structures intact, (2) a lateral collateral ligament (lcl) graft tensioned to 10 or 30 N, (3) a lateral collateral ligament graft tensioned to 30 N and a popliteus (pop) graft tensioned to 10 or 30 N, and (4) a lateral collateral ligament graft tensioned to 30 N and a popliteofibular (pfl) graft tensioned to 10 or 30 N. Sample standard deviations are indicated by error bars. P < 0.05 indicates a significant difference and ns indicates no significant difference between test conditions at the indicated degrees of flexion.

Discussion

Materials and Methods | Results | Discussion | Acknowledgements | References

In this study, we measured the abilities of posterolateral reconstructions to limit external tibial rotation and alter forces in a posterior cruciate ligament graft in response to an applied external tibial torque. Variables that were investigated included the amount of tension applied to the grafts and the effects of free compared with locked tibial rotation during graft tensioning. On the basis of preliminary testing with these graft configurations, we selected 10 N as the minimum tension that could be reliably applied to the graft, whereas 30 N was thought to be a reasonable amount that would be applied to a posterolateral graft in clinical practice. With our test apparatus, the tibia could be rigidly locked during graft tensioning to simulate the position during surgery with the tibia and/or foot held manually. The rotations and graft forces measured in this study would have relevance for the immediate postoperative period. Relaxation of tension in all grafts after in vivo cyclic loading would be expected with time, which could result in greater external rotations than were measured here^24,25.

Protocols for tensioning posterolateral grafts are not well described in the literature. Lee et al.²¹ tensioned a split graft used to reconstruct the lateral collateral and popliteofibular ligaments with the knee at 30° of flexion with internal rotation. Sekiya and Kurtz²² also utilized a split graft tensioned at 30° with valgus stress and an internal tibial torque. Stannard et al.²³ described a modified two-tailed technique for reconstruction of the popliteus and the lateral collateral ligament: the graft was tensioned with the knee flexed to 30° and the foot internally rotated. None of these authors mentioned the level of graft tension that was applied or the amount of internal tibial rotation when the graft was tensioned.

On the basis of these reports, we chose to tension the posterolateral grafts at 30° of knee flexion and to measure the amount of internal rotation as the grafts were tensioned with the tibia free and locked. We found that the greater the internal rotation after graft tensioning, the lesser the external tibial rotation with application of external tibial torque. When the tibia was held in neutral rotation during popliteus and popliteofibular graft tensioning, there was significantly less internal rotation than there was when the tibia was free to rotate. The internal rotation that did occur was due to a "spring-back" effect produced by the inherent elasticity of the graft tissues, which pulled the tibia into internal rotation as it was released—that is, applying tension to the posterolateral graft (with the tibia locked) caused it to elongate; when the tibia was fixed, the graft tissue remained under strain. When the tibia was unlocked, the tissue strain relaxed as the tibia rotated internally from the position at which the graft was tensioned.

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Fig. 5: Mean curves of tibial rotation versus knee flexion angle produced by application of passive knee extension (with the lateral collateral ligament [lcl] intact) in the fifteen knees, with (1) all posterolateral structures intact, (2) a popliteus (pop) graft tensioned to 30 N with free or locked tibial rotation, and (3) a popliteofibular (pfl) graft tendon tensioned to 30 N with free or locked tibial rotation. Sample standard deviations are indicated by error bars. P < 0.05 indicates a significant difference between test conditions.

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Fig. 6: Mean curves of resultant force versus knee flexion angle produced by application of 5 N-m of external tibial torque in the fifteen knees, with the posterior cruciate ligament (pcl) intact and with a posterior cruciate ligament graft and (1) all posterolateral structures intact, (2) a lateral collateral ligament (lcl) graft tensioned to 10 or 30 N, (3) a lateral collateral ligament graft tensioned to 30 N and a popliteus (pop) graft tensioned to 10 or 30 N, and (4) a lateral collateral ligament graft tensioned to 30 N and popliteofibular (pfl) graft tensioned to 10 or 30 N. Sample standard deviations are indicated by error bars. ns = no significant difference between test conditions at the indicated degrees of flexion.

It should be noted that our cadaveric model did not include the inherent passive tension in the knee muscles that would be present in vivo at the time of surgery. The amount of internal tibial rotation produced by graft tensioning in vivo could be less than what was measured in this study, as a result of passive resistance from the knee muscles. We believe that our results indicate the maximum amount of tibial rotation that could occur.

The normal knee has an inherent external rotatory laxity at 30° due to slackening of the native posterolateral structures with knee flexion^16,17. Most surgeons test for external rotatory laxity at the time of graft tensioning. However, the correct amount of laxity is difficult to judge, and it is possible that the natural rotatory laxity of the knee may be reduced or eliminated with the graft in place. It is possible that physioglogic external rotatory laxity may return as the posterolateral grafts stretch out during the healing process, as a result of repeated cyclic loading. However, the clinical effects of excessive internal prerotation of the tibia at the time of graft tensioning are unknown.

In vivo, control of external tibial rotation is provided by the popliteus muscle acting at its tendinous insertion on the femur. In our cadaveric model, some ofthe muscle attachment of the popliteus to the tibia was cut while the tibial inlay was placed. This left the femoral insertion of the popliteus tendon as well as some of its fascialattachments intact. Detaching the popliteus tendon from the femur significantly increased external tibial rotation. This was likely due to its attachment to other structures, including its connection to the fibula through the popliteofibular ligament. Therefore the popliteus complex provides both static and dynamic restraint to external tibial rotation. Clinically, detachment of the popliteus tendon from the lateral femoral condyle is commonly observed with a Grade-3 injury to the posterolateral corner^26,27.

At the time of surgery, a ruptured lateral collateral ligament is normally recognized and reconstructed to restore varus laxity. Detachment of the popliteus tendon from the lateral femoral condyle and a tear of the popliteofibular ligament can be more difficult to appreciate. When all three structures were absent in conjunction with a posterior cruciate ligament injury, reconstruction of the posterior cruciate ligament alone was not sufficient to restore posterior cruciate graft forces to normal levels or to restore normal external tibial rotations between 0° and 25° of knee flexion. Theoretically, a popliteofibular graft should be more effective in controlling external rotation than a popliteus graft because it is fixed at a greater distance from the axis of tibial rotation, thus giving it a greater mechanical advantage. This was not observed in our study: both grafts had equivalent effects at the same level of pretension. However, the mean posterior cruciate graft forces associated with a popliteofibular reconstruction were approximately 10 to 20 N less than those associated with a popliteus reconstruction beyond 60° of flexion.

As a result of differences in graft-tensioning protocols and the combinations of posterolateral graft reconstructions tested, our results differ somewhat from those in prior studies. Kanamori et al.⁸ found that knees subjected to 10 N-m of external tibial torque after reconstruction of the popliteofibular ligament had external rotation values that were not significantly different from those in the intact knee. An unspecified level of tension was applied to the popliteofibular graft at 30° of knee flexion, and the posterior cruciate ligament and lateral collateral ligament were not reconstructed. Nau et al.¹⁷ found that reconstructions of the posterior cruciate ligament and the popliteus tendon as well as reconstructions of the posterior cruciate ligament, popliteus tendon, and popliteofibular ligament restored external rotations to normal at 30° and 90° of knee flexion with 5 N-m of external torque. The posterolateral grafts were tensioned to 10 N with the knee at 90°, and the tibia internally rotated 10°. The posterior cruciate graft was tensioned to 70 N at 90°. Nau et al.¹⁶ performed external torque tests with reconstructions of the lateral collateral and popliteofibular ligaments as well as reconstructions of the lateral collateral ligament, popliteofibular ligament, and popliteus tendon; the posterior cruciate ligament was intact. All posterolateral graft combinations restored normal external tibial rotations at 30° and 90° of knee flexion. The popliteofibular and popliteus grafts were tensioned to 10 N at 30° of flexion, with the tibia in neutral rotation. The lateral collateral ligament graft was tensioned to 10 N at 90°, with neutral tibial rotation. Sekiya et al.¹⁸ reconstructed the popliteus tendon and the popliteofibular ligament in knees with a double-bundle reconstruction of the posterior cruciate ligament. External tibial rotations (with application of 5 N-m of torque) were not significantly different from those of the intact knee. Both posterolateral graft reconstructions were tensioned to 67 N at 30° of flexion. Addition of the posterolateral reconstructions to an isolated double-bundle reconstruction of the posterior cruciate ligament significantly decreased external tibial rotation at 0°, 30°, and 90° of knee flexion but decreased force in the posterior cruciate ligament reconstruction at 90° only.

The present in vitro study had several limitations. The tibial rotations and graft forces measured in this study would be comparable with those present at the time of surgery. Missing from our experimental protocols were the effects of weight-bearing and muscle forces. With the graft-tensioning protocols used in this study, reconstructions of the lateral collateral ligament and the popliteus tendon and those of the lateral collateral and popliteofibular ligaments resulted in marked overconstraint of external rotation compared with that of the intact knee. For example, the mean rotations with those reconstructions tensioned to 30 N were 3° to 10° less than the mean rotations with all posterolateral structures intact. Clearly, the graft-tensioning protocols used in the present study were unable to restore both graft forces and external tibial rotations to normal. Our study was designed to directly compare reconstruction of the popliteus tendon with that of the popliteofibular ligament by utilizing the same graft for both reconstructions. It was not possible to test both reconstructions simultaneously. It is likely that reconstruction of all three posterolateral structures would overconstrain external tibial rotation to an even greater degree. More studies are required to develop other graft-tensioning protocols that more closely replicate normal external rotatory laxity.

In conclusion, our study demonstrated that the knee is highly unstable with all posterolateral structures removed: the mean maximum tibial rotations and posterior cruciate ligament graft forces were nearly 30° and 200 N, respectively. Reconstruction of the lateral collateral ligament alone was insufficient to restore normal posterior cruciate force levels. Addition of a reconstruction of the popliteus tendon or popliteofibular ligament to a reconstruction of the lateral collateral ligament significantly reduced forces in the posterior cruciate ligament graft to normal (or below-normal) levels and markedly reduced external tibial rotation by approximately 7° (in 0° of flexion) to 13° (in 90° of flexion) (p < 0.05). External tibial rotations associated with reconstructions of the lateral collateral ligament and popliteus tendon were equivalent to those associated with reconstructions of the lateral collateral and popliteofibular ligaments, and both were significantly less than those in the intact knee (i.e., the reconstructed knee was overconstrained). Increasing tension in either a popliteus or a popliteofibular graft from 10 to 30 N significantly decreased mean tibial rotations approximately by 2° to 3°. Further research in this important area is warranted to determine optimum graft tensioning that will better restore normal graft forces and knee kinematics. ?

Acknowledgements

Materials and Methods | Results | Discussion | Acknowledgements | References

Note: Human tissues utilized for this study were provided by the Musculoskeletal Transplant Foundation.

References

Materials and Methods | Results | Discussion | Acknowledgements | References

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Topics

knee joint ; ligaments ; posterior cruciate ligament ; reconstructive surgical procedures ; tibia ; torque ; tissue transplants ; transplantation ; lateral collateral ligament, knee ; popliteus muscle structure

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Keith L. Markolf, Benjamin R. Graves, Susan M. Sigward, Steven R. Jackson, David R. McAllister; Effects of Posterolateral Reconstructions on External Tibial Rotation and Forces in a Posterior Cruciate Ligament Graft. The Journal of Bone & Joint Surgery. 2007 Nov;89(11):2351-2358.

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