Orthopedics

Feature Article 

Preservation of the Tibial Remnant in Anterior Cruciate Ligament Reconstruction May Improve Postoperative Proprioceptive Function

Byung-Ill Lee, MD, PhD; Chang Hyun Kim, MD; Byung Woong Jang, MD; Yong Cheol Hong, MD; Sai-Won Kwon, MD, PhD

Abstract

The purpose of this study was to retrospectively compare clinical results, including proprioceptive function, after anterior cruciate ligament (ACL) reconstruction between 2 groups using techniques that preserve and eliminate the tibial remnant. Forty-eight patients who were followed for at least 24 months after ACL reconstruction with 4-strand hamstring tendon autografts were enrolled in this study. They were then divided into 2 groups: the remnant-preserving group (group A, 26 patients), in whom more than 7 mm of the remnant tibial stump (approximately 20% of the mean length of the ACL) was preserved; and the remnant-eliminating group (group B, 22 patients), in whom the tibial remnant was eliminated during ACL reconstruction. The average duration of follow-up was 25.5 months. At last follow-up, patients were evaluated using the International Knee Documentation Committee scale, Hospital for Special Surgery score, Lachman test, arthrometer, reproduction of passive positioning (RPP) test, threshold to detection of passive motion (TTDPM) test, one-leg hop test, and single-limb standing test. The clinical results between the 2 groups were statistically compared. Group A showed significantly better results on the RPP test at 15° (P=.040) and 30° (P=.010), one-leg hop test (P=.017), and single-limb standing test (P=.007) compared with group B. The other results showed no significant differences. The remnant-preserving technique in ACL reconstruction yields better proprioceptive and functional outcomes and may help achieve postoperative patient satisfaction. [Orthopedics. 2020;43(x):xx–xx.]

Abstract

The purpose of this study was to retrospectively compare clinical results, including proprioceptive function, after anterior cruciate ligament (ACL) reconstruction between 2 groups using techniques that preserve and eliminate the tibial remnant. Forty-eight patients who were followed for at least 24 months after ACL reconstruction with 4-strand hamstring tendon autografts were enrolled in this study. They were then divided into 2 groups: the remnant-preserving group (group A, 26 patients), in whom more than 7 mm of the remnant tibial stump (approximately 20% of the mean length of the ACL) was preserved; and the remnant-eliminating group (group B, 22 patients), in whom the tibial remnant was eliminated during ACL reconstruction. The average duration of follow-up was 25.5 months. At last follow-up, patients were evaluated using the International Knee Documentation Committee scale, Hospital for Special Surgery score, Lachman test, arthrometer, reproduction of passive positioning (RPP) test, threshold to detection of passive motion (TTDPM) test, one-leg hop test, and single-limb standing test. The clinical results between the 2 groups were statistically compared. Group A showed significantly better results on the RPP test at 15° (P=.040) and 30° (P=.010), one-leg hop test (P=.017), and single-limb standing test (P=.007) compared with group B. The other results showed no significant differences. The remnant-preserving technique in ACL reconstruction yields better proprioceptive and functional outcomes and may help achieve postoperative patient satisfaction. [Orthopedics. 2020;43(x):xx–xx.]

Success in anterior cruciate ligament (ACL) reconstruction means achieving both mechanical stability and patient satisfaction. However, mechanical stability is not always correlated with patient satisfaction and functional outcomes.1–4 Some authors have reported that patient satisfaction after reconstruction is closely correlated with knee proprioception.5–7

In most cases, ACL ruptures occur in the proximal half.8 According to Schutte et al,9 most mechanoreceptors are located in the subsynovial layer near the tibial insertion of the ligament. Ochi et al10 have shown that sensory reinnervation occurs in the reconstructed ACL. Because ACL mechanoreceptors are related to proprioception, preserving the tibial remnant of the ruptured ACL could be a potential source of reinnervation of the implanted ACL graft and restoration of proprioceptive function.

Proprioceptive function and subjective sensation cannot be analyzed using only objective assessments, such as the Hospital for Special Surgery (HSS) score, International Knee Documentation Committee (IKDC) scale, or physical examination. There are a few methods for evaluating knee joint proprioception, and functional disabilities resulting from ACL injuries have been reported using these methods.11,12 However, only the proprioceptive changes between ACL-injured knees and normal uninjured knees were compared.

This study sought to retrospectively compare clinical outcomes, including proprioceptive function, between remnant-preserving and remnant-eliminating ACL reconstructions.

Materials and Methods

This study received institutional review board approval. From January 2013 to January 2015, a total of 60 patients underwent arthroscopic ACL reconstruction via hamstring autografting using TightRope (Arthrex, Naples, Florida) for proximal fixation. All patients were operated on by single surgeon (B.-I.L.) using the same technique, and their medical records and operation videos were reviewed retrospectively. The exclusion criteria were as follows: history of operation on the injured knee, more than 2 multiple ligament injuries, period of more than 6 months from injury to operation, articular cartilage lesions grade 3 or more, and meniscal injuries that underwent subtotal or total meniscectomy.

Forty-eight patients were followed for more than 24 months. The mean duration of follow-up was 25.5 months (range, 24–36 months). Of the selected patients, 36 were men and 12 were women, with a mean age of 30.7 years. The associated injuries included lateral meniscal injuries (23 cases), medial meniscal injuries (11 cases), and both (7 cases). Eight cases were repaired, and 10 cases were meniscectomized partially. Twenty-eight cases were acute (<3 months), and 20 were chronic (>3 months).

The length of the tibial remnant was measured using a 3.5-mm–tipped probe during the operation. The known mean ACL length is 38 mm.13 The remnant-preserving group (group A) consisted of 26 patients with an ACL remnant of more than 7 mm (approximately 20% of the mean length of the normal ACL) (Figure 1), and the remnant-eliminating group (group B) consisted of 22 patients. Patient demographics are presented in Table 1. The authors conducted a thorough analysis of the last follow-up findings and compared the results between the 2 groups retrospectively.

Arthroscopic view of the proximal ruptured anterior cruciate ligament with the remnant more than 7 mm (approximately 20% of the mean length of the anterior cruciate ligament) (A) and graft covered by tibial remnant after reconstruction (B).

Figure 1:

Arthroscopic view of the proximal ruptured anterior cruciate ligament with the remnant more than 7 mm (approximately 20% of the mean length of the anterior cruciate ligament) (A) and graft covered by tibial remnant after reconstruction (B).

Patient Demographics

Table 1:

Patient Demographics

Surgical Technique

The semitendinosus and gracilis tendons were harvested after the arthroscopic intra-articular examination was performed. In the cases where the tibial remnant was more than 7 mm, the tibial tunnel was positioned within the normal ACL tibial remnant boundaries for anatomic graft placement. A tibial drill guide was positioned in the center of the remaining ACL footprint. The guidewire was advanced into the joint and carefully directed in line with the ACL remnant and just lateral to the posterior cruciate ligament (PCL), thus ensuring that there would be no roof or wall impingement. If the location of the guidewire was satisfactory, reaming was started using a small cannulated reamer, followed by sequential tibial tunnel drilling using a larger reamer. The subchondral bone of the far cortex was drilled using a reamer, which was stopped at the ACL stump base with care while not damaging the tibial stump. The tibial remnant was eliminated in the rest of the cases. Further, the femoral tunnel was created at a depth of 25 mm with the outside-in technique using the FlipCutter (Arthrex) as a retrograde drill in all cases. Thereafter, the ACL graft was passed through the tibial tunnel toward the femoral tunnel. In group A, the ACL graft was passed through the tibial remnant's internal diameter. Once the ACL graft passed through the femoral tunnel, it was pulled up tightly and fixed using TightRope. Tibial fixation was performed using bioabsorbable interference screws (BIOCRYL; DePuy Mitek Inc, Raynham, Massachusetts) of the same diameter as the tunnel while 30 lb of tension was laterally applied from the tibial tunnel for pulling; it was then reinforced using a spiked washer screw.

Immediately after the operation, the patients performed quadriceps muscle– setting and straight leg–raising exercises while wearing a supportive brace during knee extension. From 1 week after surgery, the patients were permitted to perform range of motion (ROM) exercises as tolerated but not an active rehabilitation program with hyperextension exercises. The patients were permitted to perform partial weight-bearing ambulation from the second week while wearing a functional brace, along with full ROM exercises. The patients continued muscle-strengthening exercises, and both brace removal and full weight-bearing ambulation on the flat floor were permitted 6 weeks postoperatively.

The objective evaluations conducted to check joint stability included the Lachman test and the manual maximum displacement test using a KT-2000 arthrometer (MEDmetric, San Diego, California). For the subjective tests, the IKDC scale and HSS score were used. Functional assessments, such as the reproduction of passive positioning (RPP) test, threshold to detection of passive motion (TTDPM) test, one-leg hop test, and single-limb standing test, were conducted by another physician (S.-W.K.) who was blinded to patient characteristics. Testing was conducted in a blinded manner; that is, both knees were covered with long pants to avoid allowing the examiner performing the test to know which leg had been injured. The RPP test is a modified method designed by Barrett et al14 that uses a Thomas splint and a Pearson attachment. The patients were provided with a flexion device to raise the knee joint at a flexed position (15°, 30°, and 45°), with 5 seconds to memorize the angle. Thereafter, the Pearson attachment was removed at the peak extension point after 15 seconds, and the patients were instructed to return to the memorized angle actively. At this point, discrepancy between the reproduced angle and the original angle was measured 5 times after 2 sets of exercises to obtain the mean for both the normal and the ACL-reconstructed knees. The TTDPM test was conducted to determine the threshold to detect a slow passive change in the knee joint position.11 The patients were tested in continuous passive motion (CPM). The patients were blindfolded and deafened during examination. The knee joint angle with CPM was started at 15°, 30°, and 45° and was slowly moved into the direction of extension at a speed of 0.5°/s. An examiner measured the angle when the patients recognized the first change in the angle. The TTDPM test was conducted twice in all cases, and the entire process was completed 5 times to obtain the mean results for the normal and reconstructed knees.

For statistical analyses, the authors used the Mann–Whitney U test and Pearson correlation. The confidence interval was set at 95%.

Results

The Lachman test findings were slightly positive (+) in 5 patients and moderately positive (++) in 2 patients in group A and slightly positive (+) in 3 patients and moderately positive (++) in 1 patient in group B postoperatively. The KT-2000 arthrometer was employed to determine the manual maximum displacement; group A had a mean displacement of 2.5±1.0 mm, which was higher than that of the normal knees, whereas group B had a mean displacement of 2.1±1.2 mm postoperatively. However, all objective test findings showed no significant difference between the 2 groups.

Preoperative HSS score improved at the postoperative assessment. Mean HSS score improved from 70.8 to 92.8 in group A and from 73.1 to 93.8 in group B at the last follow-up, with no significant difference between the 2 groups. The IKDC scale findings did not show significant differences between the 2 groups (Table 2).

International Knee Documentation Committee Grading According to the Amount of Preserved Remnant

Table 2:

International Knee Documentation Committee Grading According to the Amount of Preserved Remnant

When the RPP test was conducted at 15° (P=.040) and 30° (P=.010), group A showed good results with significance. At 45°, group A showed better results without significance as compared with group B. The TTDPM test showed better results in group A at 15°, 30°, and 45°, although there was no significance (Table 3). For the one-leg hop test, group A showed a mean rate of functional recovery (compared with the normal side) of 87% compared with 82% in group B. A significant improvement was identified in group A (P<.05). The single-limb standing test showed better results in group A with significance (P<.05) (Table 4).

Comparisons of Results of Reproduction of Passive Positioning and Threshold to Detection of Passive Motion Between the 2 Groups

Table 3:

Comparisons of Results of Reproduction of Passive Positioning and Threshold to Detection of Passive Motion Between the 2 Groups

Results of the One-Leg Hop Test and Single-Limb Standing Test

Table 4:

Results of the One-Leg Hop Test and Single-Limb Standing Test

Discussion

In recent years, it has been accepted that the normal ACL is innervated by mechanoreceptors and has an important role in proprioceptive sensation, and interest has moved to the ACL's proprioceptive and joint-stabilizing functions.15 In other words, ACL injury not only causes mechanical instability but also leads to a functional deficit in the form of diminished knee joint proprioception. Thus, restoring proprioception may be just as important as restoring knee mechanical stability. Kennedy et al16 emphasized that joint instability and secondary injuries may be due to the loss of proprioception in the event of ACL damage. Further, Valeriani et al17 reported that the surgical results for mechanical stability after ACL reconstruction are not always consistent with the degree of patient satisfaction or the functional knee joint recovery. Even when the mechanical integrity has been restored after ACL reconstruction performed on highly unstable patients, some reconstructions still yield functional instability during sports activities.18 It means that if there is permanent loss of ACL mechanoreceptors, which are responsible for proprioception, afferent neurological information from the ACL is not restored, although joint stability is achieved after ligament reconstruction. Proprioceptive sensation also has an important role in preventing the progression of joint degeneration.14

The presence of mechanoreceptors in the ACL is well documented.9,19–23 Proprioceptive nerve fibers, such as Golgi tendon organs, Pacinian corpuscles, and Ruffini endings, have all been identified within the ACL.24 These mechanoreceptors mediate the sense of joint position and motion, as well as possibly contribute to a reflex arc of stabilizing muscular contractions.25 A majority of these receptors have been reported to be located within the distal aspect of the ACL near the tibial insertion site.20 All of these previous studies hypothesized that the ACL, as a significant sensory organ, functions not only as a provider with proprioceptive information, but also as an initiator of protective and stabilizing muscular reflexes. Thus, if the mechanoreceptors remain functional in the ruptured ACL remnant, they may become a source for reinnervation of the reconstructed graft and will be of help to patients.

There are some histological studies on the ruptured ACL remnants that investigated mechanoreceptors or proprioceptive fibers.1,26–28 Georgoulis et al3 reported that mechanoreceptors would be found even 3 years after injury in patients with an ACL remnant readapted to the PCL. They concluded that leaving the ACL remnants might be potentially beneficial to patients for whom remnant tissue preservation is surgically possible. Ochi et al29 found a better joint position sense in patients with a conserved part of the native ACL. The presence of proprioceptive mechanoreceptors in the ACL remnants and their importance for possible reinnervation of ACL grafts were pointed out in an immunohistochemical study by Lee et al.27 In a study of microscopic observations of the remnants obtained from ACL-injured patients, Gao et al30 found various mechanoreceptors, which decreased in number and size from the time of injury to surgery. Although the study did not offer direct proof of the benefits of remnant-preserving ACL reconstruction, it suggested that preservation of these mechanoreceptors would benefit recovery of proprioception, and this result could provide a theoretical basis for clinical studies.

To prove the proprioceptive improvement using the remnant-preserving technique, a proprioception test was used in this study. Investigators used 2 types of tests to measure proprioception: 1 that ascertains the TTDPM (movement sense) and 1 that examines the capacity to reposition the limb accurately (position sense). However, given the complexity of proprioception, neither test is ideal. Many of these early tests were confounded by muscle or skin receptor disturbances. Further, these mechanoreceptors were also found in other structures of the knee joint.31,32 The findings of studies on proprioception should be interpreted in the broader context of whether joint or muscle mechanoreceptors play the primary role in proprioception. None of the current tests for proprioception allow differentiation between the ACL mechanoreceptors and the remaining mechanoreceptors of the capsule and muscles surrounding the knee; thus, the reported tests generally cannot produce conclusive information regarding the functional importance of ACL mechanoreceptors. There may not be sound rationale to justify the extremely slow rate of knee displacement of 0.5°/s in most studies. The detection of movement at this rate may not truly assess proprioception. New tests are necessary to investigate the relevant roles of the sensorimotor system after ACL injury.33

There were few studies on the proprioceptive function of the ACL. Fremerey et al34 used the RPP test to confirm that proprioception is associated with the patient's functional satisfaction. Their study was meaningful in that they investigated the differences and the changes with time of proprioception by comparing patients with acute ACL injuries and patients who underwent reconstruction after chronic ACL injuries to normal knees. However, unlike the current study, they did not evaluate the effects of remnant preservation on the proprioception. Chouteau et al35 reported good results of ACL reconstruction with preservation of partially ruptured remnants. They evaluated proprioception in a newly developed system but did not analyze the superiority of remnant preservation over remnant elimination. Compared with these studies, the advantage of the current study is that it has proved that preserving the remnant actually helps to restore postoperative proprioception rather than eliminating it.

The benefits of preserving the ACL tibial remnant remain unclear. Takazawa et al36 reported that ACL remnant preservation could facilitate functional recovery and decrease graft rupture after reconstruction. In contrast, 2 recent meta-analyses showed that ACL reconstruction using the remnant-preserving technique yields similar outcomes in terms of anterior stability and functional recovery.37,38 However, in the current study, preserving the ACL remnant yielded better outcomes than eliminating it.

This study had many limitations. One was the small number of patients, which may reduce the power of the study. Also, the authors did not perform any pre or post hoc power analyses. Further, the duration of follow-up—25.5 months—was relatively short. And, as discussed, the method for evaluating proprioception is difficult and complicated. Further research is required that can exclude the effects of other mechanoreceptors involved in knee motion and evaluate the effects of the ACL alone on proprioception. Additionally, long-term follow-up studies with a larger number of patients are needed. Nevertheless, this study is meaningful because to the authors' knowledge it is the first to evaluate the possibility of the advantage of remnant-preserving techniques for proprioceptive function based on a proper study design.

Conclusion

This study supports that the remnant-preserving technique in ACL reconstruction yields better proprioceptive and functional outcomes than the remnant-eliminating technique. However, more significant differences in proprioceptive tests should be identified through further studies with larger numbers of patients.

References

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Patient Demographics

CharacteristicGroup A (n=26)Group B (n=22)
Age, mean±SD, y31.4±10.230.0±11.0
Sex, men/women, No.19/717/5
Cause of injury, No.
  Sports activities1714
  Traffic accident77
  Fall21
Associated injury, No.
  Medial meniscus tear56
  Lateral meniscus tear1310
  Both meniscus tear43

International Knee Documentation Committee Grading According to the Amount of Preserved Remnant

GradeaNo. of Patients

Group A (n=26)Group B (n=22)
A97
B1514
C21
D00

Comparisons of Results of Reproduction of Passive Positioning and Threshold to Detection of Passive Motion Between the 2 Groups

Test AngleMean±SDP

Group AGroup B
Reproduction of passive positioning
  15°0.69°±0.56°1.36°±1.04°.040a
  30°0.43°±0.37°1.34°±0.84°.010a
  45°0.75°±0.52°1.72°±1.01°.056
Threshold to detection of passive motion
  15°0.71°±0.62°1.33°±1.10°.066
  30°1.18°±0.79°1.60°±0.87°.975
  45°1.30°±1.19°1.86°±1.30°.617

Results of the One-Leg Hop Test and Single-Limb Standing Test

TestGroup AGroup BP
One-leg hop, % functional recovery86.5%82.1%.017a
Single-limb standing, mean±SD, min0.35±0.230.48±0.34.007a
Authors

The authors are from the Department of Orthopaedic Surgery (B-IL, BWJ), Soonchunhyang University Hospital Seoul, Seoul, and the Department of Orthopaedic Surgery (CHK, YCH, S-WK), Soonchunhyang University Hospital Cheonan, Cheonan, Korea.

Drs Lee and Kim contributed equally to this study and should be considered as equal first authors.

The authors have no relevant financial relationships to disclose.

The authors thank the Soonchunhyang University Research Fund for support.

Correspondence should be addressed to: Sai-Won Kwon, MD, PhD, Department of Orthopaedic Surgery, Soonchunhyang University Hospital Cheonan, 31, Suncheonhyang 6-gil, Dongnam-gu, Cheonan, Korea, 31151 ( osos@schmc.ac.kr).

Received: December 30, 2018
Accepted: April 03, 2019
Posted Online: April 09, 2020

10.3928/01477447-20200404-04

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