Proprioception and Anterior Cruciate Ligament Reconstruction

Chapter 68 Proprioception and Anterior Cruciate Ligament Reconstruction

Many modern rehabilitation programs for patients who have undergone anterior cruciate ligament (ACL) reconstruction incorporate exercises and drills that are directed toward improving neuromuscular function and coordination. They are often loosely referred to as proprioceptive training exercises. This chapter explores the basis for the incorporation of such exercises into rehabilitation following ACL reconstruction.

The human ACL has been shown to contain mechanoreceptors including Golgi tendon organs, Pacinian corpuscles, and Ruffini nerve endings.^1,2 These receptors contribute to proprioception about the knee joint and are also believed to form part of a reflex arc in which an anterior displacement of the tibia results in hamstring muscle contraction. Such a reflex presumably serves to protect the knee, and the ACL in particular, from such stresses. ACL rupture can therefore be expected to result in disruption or alterations of these pathways.

The term proprioception has proved difficult to define succinctly and has similarly been tested and measured by a variety of techniques. The definition of proprioception is generally agreed to include joint position sense and the ability to detect joint movement (kinesthesia). These have been measured by joint position matching tasks and by threshold to detection of passive movement tasks, respectively. Overall, it appears that threshold to detection methods have proved more reliable, although the two types of tests address different aspects of proprioception.

Another approach has been to use tests of neuromuscular function. These involve both afferent and efferent components and therefore test not only proprioception but also the muscular response. Examples of such tests are (1) measurement of latency of hamstring muscle contraction following the application of an anterior displacement force to the tibia and (2) stabilometric tests in which the movement of the center of pressure is measured during a single leg stance. More global functional tests include the various hop tests.

When assessing proprioception or neuromuscular function following ACL rupture and subsequent reconstruction, some fundamental issues need to be considered. Because alterations in the uninjured limb have been reported by some authors, it is important to include a group of control subjects. Longitudinal studies are probably of greater benefit than studies using only one point in time, as deficits have been demonstrated to change over time following both injury and reconstructive surgery. The type of graft used is also relevant for tests involving a hamstring muscle response.

Using a threshold to detection of passive movement test, Barrack et al³ demonstrated a significantly higher threshold value in ACL deficient limbs compared with the normal contralateral limb in a group of 11 patients tested 3 months following ACL rupture. A group of control subjects showed virtually identical threshold values for both knees. The higher threshold values were attributed to a loss of proprioceptive function. Numerous authors have also described the presence of deficits attributable to loss of proprioception in ACL deficient knees, whereas some authors have shown no differences between injured and contralateral or healthy control subject knees (for review, see Reider et al⁴). For instance, Pap et al⁵ found a higher rate of failure to detect passive movement in ACL deficient knees compared with the contralateral knee or healthy control subjects’ knees. However, unlike Barrack et al, they did not find any difference in the threshold to detect passive movement among any of the knees.

Beard et al⁶ measured the latency of reflex hamstring contraction in response to an anteriorly directed shear force to the upper calf in 30 patients with an ACL rupture. They found significantly greater latencies in the ACL deficient knees compared with the contralateral knees. Interestingly, the frequency of giving-way episodes reported by the patients correlated with the latency differential between their two limbs.

Many authors have evaluated proprioception following ACL reconstruction, but they have reported conflicting results. This may be due in part to the different methodologies employed. Various tests of proprioception have been used (joint position sense, threshold to detect passive movement, reaction time, and stabilometric testing). ACL reconstructed knees have been compared with either the contralateral knee, healthy control subject knees, or in some instances to both. Most studies have evaluated patients at only one time point, although some have followed patients over time from preoperatively to as long as 3.5 years postoperatively. The results of studies that have either used a control group of subjects or provided longitudinal follow-up have been summarized in Tables 68-1 and 68-2.

Table 68-1 Studies Comparing Proprioception Between Patients after Anterior Cruciate Ligament Reconstruction (ACLR) and Controls

F, Female; HS, hamstring; M, male; PT, patellar tendon.

From Table 68-1 it can be seen that the ACL reconstructed knees have been shown to be either equivalent to or worse than healthy control subject knees. The length of follow-up does not appear to explain the disparate findings. Four of the five studies that found no difference used joint position sense as a measure of proprioception, whereas only two of the five studies that found the ACL reconstructed knees to be inferior used this method of testing proprioception.

Two of the longitudinal studies used joint position sense as a measure of proprioception, whereas one used threshold to detect passive movement and another used both joint position sense and threshold to detect passive movement. Iwasa et al⁷ evaluated joint position sense in 38 subjects before ACL reconstruction using a hamstring tendon graft and every 3 months after surgery to 24 months. There was an improvement in joint position sense from 9 months through 18 months, but there was a small group of eight in whom joint position sense did not improve. A correlation was observed between better stability and better joint position sense.

Fremerey et al⁸ measured joint position sense in 20 patients with chronic ACL deficiency who underwent a patellar tendon ACL reconstruction as well as in 20 control subjects and 20 patients with an acute ACL rupture. Preoperatively the chronic ACL deficient knees had significantly better joint position sense than acute ACL deficient knees but were worse than control subjects’ knees. Following surgery there was an improvement, most of which occurred between 3 and 6 months. There was some further improvement at 3 years, although a small deficit remained in the operated knee for mid-range positions.

Reider et al⁴ undertook a longitudinal study of 26 patients undergoing ACL reconstruction and measured both joint position sense and threshold to detect passive movement preoperatively at 3 and 6 weeks and at 3 and 6 months postoperatively. They used both the contralateral knees as well as the knees of healthy volunteers as controls. The authors concluded that threshold to detect passive movement was a more reliable method than joint position sense for testing proprioception. In the patient group there was no significant difference in the threshold between the injured and contralateral knee at any of the time points. Both knees were significantly worse than the healthy controls preoperatively. However, both knees improved postoperatively such that they were not significantly different than healthy control knees at 6 months postoperatively.

The authors noted that improvements in proprioception were seen as early as 6 weeks following ACL reconstruction. Such a short time period is not consistent with reinnervation of the graft being the basis of the improvement. The authors, as well as Iwasa et al,⁷ suggest that the improvement is probably due to the provision of a static restraint that reduces abnormal afferent activity from the capsule and other ligaments.

A number of authors have investigated the role of rehabilitation protocols designed to improve proprioception and neuromuscular function in patents with ACL ruptures (for review, see Cooper at al⁹). Such protocols have been associated with some limited improvements in joint position sense and hop testing as well as muscle strength and subjective rating when compared with traditional strengthening programs. In a group of 50 patients with ACL deficiency, Beard et al¹⁰ compared a muscle-strengthening rehabilitation protocol with a program designed to enhance proprioception and reduce the latency of reflex hamstring contraction. The proprioceptive program was associated with greater improvements in reflex hamstring contraction latency and functional scores compared with the strengthening program.

Perhaps as a result of the use of such proprioceptive programs in patients with ACL rupture, proprioception-related exercises are now frequently included in rehabilitation programs following ACL reconstruction (for an example, see Risberg et al¹¹). However, there is very little literature on the effects of the inclusion of such exercises.

Liu-Ambrose et al¹² studied 10 patients at a minimum of 6 months following ACL reconstruction with a semitendinosus tendon graft. They were randomly allocated to an isotonic strength-training program or a proprioceptive training program. Both programs involved three sessions per week for a period of 12 weeks. The proprioceptive training program was based on previously described exercises. Progression was achieved by decreasing the base of support, decreasing the stability of the surfaces on which the exercises were performed, increasing the number of repetitions, reducing visual feedback, and increasing the speed and complexity of the tasks. Progression of the strength-training program was achieved by increased loading.

Outcome measures included average isokinetic torques for the quadriceps and hamstring muscle groups at 45 degrees/sec, two hop tests (single leg hop for distance and single leg timed hop), and the peak torque time of the hamstring muscle group. The latter is the time to generate maximal torque in response to a sudden forward movement of the dynamometer arm.

The proprioceptive training group demonstrated greater percentage gains in average isokinetic torques for concentric quadriceps contraction and eccentric hamstring contraction in the operated limb. However, it should be noted that the proprioceptive training group had lower baseline average isokinetic torque values for both quadriceps and hamstring muscle groups. This may relate to the greater proportion of females or to the shorter time from surgery in this group. There was no difference between the groups for the hop tests or in peak torque time.

In a larger study of 29 patients, Cooper et al¹³ compared two different rehabilitation protocols following primary ACL reconstruction. Thirteen subjects in each group had undergone a four-strand hamstring tendon reconstruction, with the remainder having had a patellar tendon reconstruction. The patients were randomized to one of two 6-week physiotherapy programs, commencing between 4 and 14 weeks postoperatively, once they had achieved the following criteria: ability to walk without aids, 0 to 120 degrees of range of motion in the operated knee, straight leg raising without any extensor lag, and no or minimal joint effusion.

Both physiotherapy programs consisted of two 40- to 60-minute physiotherapy sessions per week and a 1-hour home exercise program on the other days. The proprioceptive and balance exercise program was based on previously described exercises used for nonoperative management of ACL ruptures, which were adapted to suit wobble boards, mini trampolines, inflatable balance discs, and exercise balls. The strengthening program used exercises designed to improve muscular strength and endurance but did not specifically address balance or proprioception.

At the conclusion of the 6-week program there were no differences between the two groups in terms of the Cincinnati Knee Rating System, the Patient Specific Functional Scale, or range of knee motion. Three hop tests (single leg hop for distance, timed 6-meter hop, and the single leg crossover triple hop for distance) were used as an objective measure of neuromuscular function. No differences were seen between the two groups.

In both of these studies the proprioception-orientated program did not appear to confer any advantage in terms of tests of neuromuscular function. Interestingly, neither study used a specific test of proprioception, although the peak torque time test used by Liu-Ambrose et al included a sensory component. The benefits of such proprioceptive training programs therefore remain to be demonstrated.

Not only do the effects of such training need to be more clearly established, but also the question of whether proprioception per se can be trained at all still needs to be answered. As Aston-Miller et al¹⁴ have noted, scenarios in which proprioception might be improved remain largely theoretical. If proprioception can indeed be improved by training, there remains the issue of what such improvement might achieve. The time required to develop protective muscle contraction in response to a stimulus is such that successful proprioceptive training might only be able to prevent injury as a result of relatively slow provocations, rather than the more rapidly applied forces that occur in a sporting situation. Thus the aim of proprioceptive training following ACL reconstruction needs to be clarified. Is it to restore normal function, to improve function beyond the individual’s preinjury level, or to prevent reinjury? If it is the latter, perhaps it is the improved patterns of muscular contraction as well as the awareness of and attention to various cues that are the real benefits of such training. Clearly, further studies are required to establish the role of proprioceptive training following ACL reconstruction.

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