Unusual pattern of injuries following knee hyperextension: a case report

Functional Interaction of the Cruciate Ligaments, Posteromedial and Posterolateral Capsule, Oblique Popliteal Ligament, and Other Structures in Preventing Abnormal Knee Hyperextension

BACKGROUND

The ligaments and soft tissue capsular structures of the knee joint that provide a resisting force to prevent abnormal knee hyperextension have not been determined. This knowledge is required for the diagnosis and treatment of knee hyperextension abnormalities.

PURPOSE

To determine the resisting moment of knee ligament and capsular structures that resist knee hyperextension.

HYPOTHESIS

The combined posteromedial and posterolateral capsular structures function to provide a major restraint to prevent abnormal knee hyperextension. The anterior and posterior cruciate ligaments resist knee hyperextension but function as secondary restraints.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A 6 degrees of freedom robotic system determined intact laxity limits in 24 cadaveric knees from 0° to 100° of knee flexion for anteroposterior limits at ±135 N, abduction-adduction limits at ±7 N·m, and external-internal limits at ±5 N·m. One loading method (n = 14 knees) used a static loading sequence with knee hyperextension to 27-N·m torque while maintaining all other degrees of freedom at zero load during sequential soft tissue cutting. The second method (n = 10 knees) used a cyclic loading sequence to decrease viscoelastic effects with soft tissue cutting at 0° of extension, followed by knee hyperextension to 27-N·m torque and cycled back to 0°. Selective soft tissue cuttings were performed of the following: oblique popliteal ligament, fabellofibular ligament, posterolateral capsule, posteromedial capsule with posterior oblique ligament, cruciate ligaments, lateral collateral ligament, popliteus, anterolateral ligament and iliotibial band, and superficial plus deep medial collateral ligaments. The sequential loss in the restraining moment with sectioning provides the function of that structure in resisting knee hyperextension.

RESULTS

The median resisting force to knee hyperextension, in descending order, was the posteromedial capsule and posterior oblique ligament (21.7%), posterorolateral ligament and fabellofibular ligament (17.1%), anterior and posterior cruciate ligaments (13% and 12.9%, respectively), superior and deep medial collateral ligament (9.6%), oblique popliteal ligament (7.7%), and lateral collateral ligament (5.4%). The combined posterior capsular structures provided 54.7% and the anterior and posterior cruciate ligaments 25.3% of the total resisting moment to prevent knee hyperextension.

CONCLUSION

Diagnosis of abnormal knee hyperextension involves a combination of multiple ligament and soft tissue structures without 1 primary restraint. The posteromedial and posterolateral capsular structures provided the major resisting moment to prevent knee hyperextension. The cruciate ligaments produced a lesser resisting moment to knee hyperextension.

CLINICAL RELEVANCE

This is the first study to comprehensively measure all of the knee ligaments and capsular structures providing a resisting moment to abnormal knee hyperextension. These data are required for diagnostic and treatment strategies on the pathomechanics of abnormal knee hyperextension in patients after injury or developmental cases.

The role of the oblique popliteal ligament and other structures in preventing knee hyperextension

BACKGROUND

Ligament restraints to terminal knee extension are poorly understood.

HYPOTHESES

(1) As with other motions of the knee, genu recurvatum is limited primarily by a named, identifiable structure. (2) As the largest static structure of the posterior knee, the oblique popliteal ligament is uniquely suited to act as a checkrein to knee hyperextension.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Twenty fresh-frozen human knees were divided into 3 groups for a ligament sectioning study. Extension moments of 14 and 27 N x m were applied before and after sectioning of each ligament, and motion changes were recorded. In group 1, the oblique popliteal ligament was sectioned first, followed by the fabellofibular ligament, ligament of Wrisberg, anterior cruciate ligament, posterolateral structures, and posterior cruciate ligament. In group 2, the order was altered to section the anterior cruciate ligament first; no other changes were made. Similarly, the cutting order for group 3 was altered to section the posterior cruciate ligament first. The sagittal tibial slope of each specimen was documented off a lateral radiograph.

RESULTS

The greatest increase in knee hyperextension was observed after sectioning the oblique popliteal ligament. This was independent of cutting order, consistent across groups, and statistically significant. In all groups, the increase in knee hyperextension after sectioning the oblique popliteal ligament approached or exceeded the increases seen after sectioning the anterior and posterior cruciate ligaments combined. Overall, less knee hyperextension was seen in knees with increased posterior tibial slope.

CONCLUSION

The oblique popliteal ligament was found to be the primary ligamentous restraint to knee hyperextension.

CLINICAL RELEVANCE

Further studies are needed to determine if surgical repair or reconstruction of the oblique popliteal ligament can restore normal motion limits in patients with symptomatic genu recurvatum. Patients with decreased posterior tibial slope would have increased recurvatum with posterior structure injury, which increases the likelihood of increased symptoms in this population.

Posterior periosteal disruption in Salter-Harris Type II fractures of the distal femur: evidence for a hyperextension mechanism

OBJECTIVE

Patterns of periosteal disruption are important factors in assessing the mechanism of injury of radiologically evident Salter-Harris (SH) fractures. The purpose of this study is to assess the frequency of posterior periosteal disruption on MRI in radiographically occult or subtle SH type II fractures of the distal femur and to evaluate associated soft-tissue findings that support a hyperextension mechanism of injury.

CONCLUSION

We found that all children in our experience with occult or subtle SH type II fractures of the distal femur have posterior periosteal disruption and other MRI findings to indicate a hyperextension mechanism of injury. Direct indicators of fracture may be inconspicuous, and the presence of posterior periosteal disruption is a clue that should prompt a search for other features of this serious pediatric injury, which may be followed by limb shortening or angular deformity.

An analysis of shoulder laxity in patients undergoing shoulder surgery

BACKGROUND

It has been recognized that there is a distinction between shoulder laxity and shoulder instability and that there is a wide range of normal shoulder laxities. Our goals were (1) to evaluate if the ability to subluxate the shoulder over the glenoid rim in patients under anesthesia would be more prevalent than the inability to do so, (2) to determine if patients with a diagnosis of instability would have significantly more shoulder laxity in the operatively treated shoulder than in the contralateral shoulder, and (3) to evaluate the observation that higher grades of shoulder laxity would be related to a diagnosis of shoulder instability. We hypothesized that, on examination with the patient under anesthesia, most shoulders could be subluxated over the glenoid rim and that the degree of shoulder laxity would be related to diagnosis.

METHODS

In the present study of 1206 patients undergoing shoulder surgery, we evaluated the symptomatic and contralateral shoulders with use of a modified anterior and posterior drawer test and a sulcus sign test, with the patients under anesthesia. The anterior and posterior translations were graded as no subluxation (Grade I), subluxation over the glenoid rim with spontaneous reduction (Grade II), or subluxation without spontaneous reduction (Grade III). The sulcus sign was graded as <1.0 cm (Grade I), 1.0 to 2.0 cm (Grade II), or >2.0 cm (Grade III).

RESULTS

When the patients were evaluated while under anesthesia, the humeral head could be subluxated over the rim anteriorly in 81.6% (984 of 1206) of the patients and posteriorly in 57.5% (693 of 1206) of the patients. When the patients were evaluated while under anesthesia, there was an increase in the laxity grade anteriorly, posteriorly, and inferiorly in 50.8%, 36.3%, and 15.8% of the patients, respectively, as compared with the preoperative assessment. For all laxity testing, the higher the grade of laxity in an anterior, posterior, or inferior direction, the greater the chance that the patient had a diagnosis of instability. Compared with Grade-I laxity, Grade-III laxity increased the odds of a diagnosis of instability in the anterior (odds ratio, 170), posterior (odds ratio, 32), and inferior (odds ratio, 10.3) directions. Compared with Grade-I laxity, Grade-II laxity increased the odds of a diagnosis of instability in the anterior (odds ratio, 9.8), posterior (odds ratio, 4.6), and inferior (odds ratio, 4.4) directions.

CONCLUSIONS

The ability to subluxate the humeral head over the glenoid rim in the patient who is undergoing shoulder surgery under anesthesia is common regardless of the diagnosis. Higher grades of shoulder laxity are associated with shoulder instability.