To the Editor:

We are writing in response to the questions raised by Dr. Starr concerning our recent publication, Surgical Management of Knee Dislocations”. We will respond to each of Dr. Starr’s questions in the order in which they were addressed in his letter.

The first question related to our decision to exclude 14 patients – four with an open dislocation, five with vascular injury requiring emergent vascular repair, three treated with external fixation and two with associated injuries (severe closed head injury and contralateral below the knee amputation). Additionally we excluded subjects if they had a varus thrust and/or mal-alignment on long-cassette radiographs. We established these exclusion criteria because of our relatively small sample size to make our population as homogeneous as possible. To do this, we eliminated potential variables that may have confounded the patient’s outcome (i.e. comorbidities or other significant injuries) and focused on a consecutive group of patients with knee dislocations that presented to our medical center. We strongly believe that the inclusion of these 14 patients with other injuries would have weakened our study.

In our study, we found that those patients who underwent acute surgical management within three weeks of injury had significantly better subjective scores and knee stability compared to those that underwent reconstruction more than three weeks after surgery. Dr. Starr questioned whether some variables other than the timing of surgery might have accounted for these observed differences. Specifically he asked if the Injury Severity Scores were equal for the two groups defined by timing of surgery. We did not have Injury Severity Scores for our subjects. Based on our inclusion/exclusion criteria we eliminated subjects with more severe injuries (i.e. head injuries, vascular injuries, amputations etc.). As stated above, this provided us with a more homogeneous group with respect to severity of injury. This also allowed us to manage all patients according to the protocol we described in the paper. Inclusion of individuals with more severe injuries would have necessitated deviations in our clinical protocol. We agree that it is possible that severity of other injuries could have adversely affected outcome. Given this, it is important for the reader to understand that our protocol for management and our conclusions apply only to obvious or occult knee dislocations in patients who do not have an open injury, vascular injury or other serious injury such as a head injury.

Dr. Starr noted that the delayed treatment group was 10 years older, on average and he questioned if this difference could have accounted for the differences observed for the subjective questionnaires. Age was not related to any of the subjective outcome measures (Lysholm, ADLS or SAS). The correlations between age and the subjective outcome measures ranged from -.09 to -.24. Despite the lack of significant correlations, in response to the concern raised by Dr. Starr, we performed an analysis of covariance (ANCOVA) in which age was entered as a covariate to statistically adjust for the effects of age. The results indicated that adjusting for age had little effect on the subjective scores for those in the acute or chronic groups and did not change our statistical conclusions.

Dr. Starr also asked if other factors, such as smoking history, social circumstances, education level or worker compensation status might have affected patient outcomes. Unfortunately we did not have these data for our subjects. It is possible that these factors could have influenced the patient’s subjective assessment of outcome. To do so, these factors would have had to satisfy two requirements: the confounding factor would have had to be related to the subjective outcome scores; and the acute and chronic groups of subjects would have had to have different levels of the confounding factor. If factors such as smoking history, social circumstances, education level, or workers compensation status met these criteria then they may have affected our results. This is an area for further research and should be part of a prospective approach to assessing outcomes following multiple ligament injury.

Dr. Starr questioned whether we tested other variables that could have influenced our observed differences between the acute and delayed treatment groups. In addition to timing of surgery, we evaluated the effects injury to the medial and lateral structures, peroneal nerve injury, tourniquet time and length of follow-up on our outcome variables. None of these variables met the above two criteria (i.e. none of these potentially confounding variables were related to any of the subjective or objective outcome variables and none of the potentially confounding variables were different in those with an acute or delayed treatment). Therefore inclusion of these confounding variables would not have affected our results. Of the variables that we collected, we were not able to find any other factors that predicted (i.e. were related with) any of the subjective or objective variables. It is possible that some variables that were not measured may have influenced subjective or objective outcome or may have affected the relationship between timing of surgery and subjective outcome. Exploration of factors that affect outcome following knee dislocation is an area for further research.

Finally Dr. Starr suggested that our results indicated that acute reconstruction of the anterior cruciate and medial collateral ligaments in the setting of a knee dislocation appeared to increase the rate of arthrofibrosis as four patients (cases 4, 7, 13 and 14) had post-operative stiffness and all of these patients had undergone acute reconstruction. All four of these patients were treated with manipulation under anesthesia. None of the patients treated after three weeks required manipulation for arthrofibrosis.

Arthrofibrosis is scarring of the joint that results in a permanent loss of motion. At the time of final follow-up, on average, there were no differences in the loss of extension or flexion or total arc of motion in those undergoing acute versus chronic reconstruction. It is true that a higher percentage of subjects undergoing acute reconstruction (4/19 vs. 0/11) required manipulation and/or arthroscopic lysis of adhesions, however early recognition and intervention for this loss of motion resulted in an acceptable range of motion at follow-up. Therefore when knee dislocations are acutely managed, careful monitoring of range of motion is necessary and the surgeon must be willing to intervene with manipulation or arthroscopic lysis of adhesions if range of motion does not progress as expected. Even if manipulation and/or lysis of adhesions is necessary, a good outcome with respect to range of motion can be expected in those undergoing acute surgical management following knee dislocation. Thus we concluded that the timing of surgery, specifically acute reconstruction of the anterior cruciate and repair of the medial collateral ligament in the setting of a knee dislocation, did not seem to increase our rate of arthrofibrosis (i.e. result in a permanent loss of motion).

We would like to thank Dr. Starr for providing us with the opportunity to address the questions that he raised regarding our study.

Sincerely

Christopher D. Harner MD

James J. Irrgang PhD PT ATC

To the Editor:

I have several questions regarding the article, “Surgical Management of Knee Dislocations” by Harner and colleagues. First, the authors excluded 14 patients - four with open dislocation, five with vascular injury requiring emergent vascular repair, three treated with external fixation, and two with associated injury (severe closed head injury and contra-lateral below-the-knee amputation). In addition, patients seen in the senior author’s clinic were excluded if they had a varus thrust on examination and/or mal-alignment on long-cassette radiographs. Do the authors have any information on how these patients were managed, or their outcome?

Next, the authors state, “The patients who were treated acutely had higher subjective scores and better objective restoration of knee stability than did patients treated three weeks or more after the injury.” So, the reader should conclude that, given two patients with similar injuries, a patient treated within 3 weeks would do better than one whose surgery is delayed beyond 3 weeks. Is it possible some other variable predisposed the delayed treatment group to poorer outcome?

Was the average Injury Severity Scores of the two groups equal,or was one group more severely injured? Others have found that ISS is a predictor of heterotopic ossification after reconstruction of dislocated knees (1). Might it affect outcome in this series as well?

The delayed treatment group was 10 years older, on average. Could this difference affect patient response to the subjective questionnaires? Might other factors affect patient responses? Smoking history? Social circumstances? Education level? Worker’s compensation status? Without these data, it’s difficult to know if these groups are equal.

In statistical testing, it appears the only variable tested against the outcome scores – the Lysholm score, the Sports Activities Scale, arc of motion, etc - was the timing of surgery. Is this correct? Or were other variables tested? If only the timing of surgery was tested as a variable it is not surprising that timing of surgery was found to be predictive of outcome.

If some unreported variable could explain the difference in outcome between the groups, might the timing of surgery be less important?

Finally, the authors note, “The timing of surgery, and specifically acute reconstruction of the anterior cruciate and medial collateral ligaments in the setting of knee dislocation, did not seem to increase the rate of arthrofibrosis in our series.” But it did, didn’t it? They noted, “Complications included postoperative stiffness in four patients (Cases 4, 7, 13, and 14; see Appendix), all of whom had undergone acute reconstruction. All four knees were treated with manipulation with the patient under anesthesia.” None of the patients treated after 3 weeks required manipulation for arthrofibrosis.

I look forward to the authors' response to these questions.

Sincerely,

Adam J. Starr, MD Department of Orthopaedic Surgery University of Texas Southwestern Medical Center 5323 Harry Hines Blvd. Dallas, TX 75390-8883 (214) 648-6428 References:

1. Heterotopic Ossification After Knee Dislocation: The Predictive Value of the Injury Severity Score. Journal of Orthopaedic Trauma. 17(5):338-345, May 2003. Mills, William J. *. Tejwani, Nirmal +.