Arch Orthop Trauma Surg (2003) 123 : 186–191 DOI 10.1007/s00402-002-0471-y

O R I G I N A L A RT I C L E

M. S. Schulz · K. Russe · A. Weiler · H. J. Eichhorn · M. J. Strobel

Epidemiology of posterior cruciate ligament injuries

Received: 11 December 2002 / Published online: 22 February 2003 © Springer-Verlag 2003

Abstract Background: The epidemiology of posterior cruciate ligament (PCL) injuries has not been well clarified. Isolated and combined PCL injuries are a frequently missed diagnosis. A better understanding of typical injury mechanisms may help in more accurate diagnosis of these injuries. Methods: In this study the epidemiology of PCL insufficiency in 494 patients was retrospectively analysed. Stress-radiography was used to quantify posterior tibial displacement. Results: The mean age at the time of injury was 27.5±9.9 years. Traffic accidents (45%) and athletic injuries (40%) were the most common injury causes. Motorcycle accidents (28%) and soccer-related injuries (25%) accounted for the main specific injury causes. The most common injury mechanisms were dashboard injuries (35%) and falls on the flexed knee with the foot in plantar flexion (24%). The mean side-to-side difference of posterior tibial displacement on posterior stress-radiographs in 90° of flexion was 13.4±4.7 mm. According to the posterior displacement values, 232 (47%) patients had isolated PCL ruptures, while 262 (53%) patients with a posterior displacement of >12 mm were classified as having a combined posterior instability. There were significantly more combined PCL lesions due to vehicular trauma as compared with athletic trauma (p<0.0001). Conclusions: In many PCL lesions, initiation of an adequate treatment regimen is delayed despite typical injury mechanisms and symptoms. In the future, a better understanding of the epidemiology of PCL injuries should enable us to diagnose

M. S. Schulz (✉) · H. J. Eichhorn · M. J. Strobel Orthopaedische Gemeinschaftspraxis Straubing, Hebbelstr. 14a, 94315 Straubing, Germany Tel.: +49-9421-995729, Fax: +49-9421-995739, e-mail: [email protected] K. Russe Department of Orthopaedics, University Hospital, Essen, Germany A. Weiler Sports Traumatology & Arthroscopy Service, Humboldt University, Berlin, Germany

the injury more reliably through a detailed history and a thorough physical and radiographic examination in the acute setting. Keywords Posterior cruciate ligament · Epidemiology · Clinical evaluation · Stress-radiography

Introduction The study of posterior cruciate ligament (PCL) injuries has attracted much less interest in the orthopaedic literature than studies of the anterior cruciate ligament (ACL) [5, 8, 22]. However, clinicians have become increasingly aware of the importance of the PCL in maintaining normal knee kinematics and function [10, 19, 21, 25]. There have been numerous recent studies of the complex anatomy and functional mechanics of the PCL, but our knowledge regarding PCL injuries is still limited [5, 9, 12, 30]. Controversies still exist with regard to the incidence, diagnosis and treatment of PCL injuries [5, 12, 20, 23, 26]. The reported incidence of PCL ruptures ranges between 1% and 44% of all acute knee ligament injuries [7, 8, 12, 20, 30]. This variability is probably due to differences in the patient populations studied, as PCL injury rates are likely to vary when comparing polytraumatized patients to an athletic population [12]. Numerous clinical tests are available for detecting and grading PCL lesions [1, 6, 22, 23], and most PCL injuries can be diagnosed in the acute phase with a detailed history and a thorough clinical examination [4, 9, 27, 29]. Nevertheless, in the past many PCL ruptures have frequently been missed in the acute phase and were first diagnosed in the chronic situation [1, 29]. In many cases the PCL injury is missed despite typical injury mechanisms and symptoms [14, 29]. However, an accurate diagnosis of the acute injury is critical to establishing a rational treatment algorithm, whether conservative or surgical [13, 14, 28, 29]. Furthermore, it is critical to distinguish between PCL lesions that are isolated and those combined with other ligament injuries, as this variable will directly affect the

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treatment and prognosis [12, 17]. To our knowledge, there has been no previous study of the demographic data and PCL injury mechanisms in a large patient population. Therefore, we retrospectively analysed our patient population to define the epidemiology of PCL lesions and to improve understanding of the typical injury mechanisms in acute and chronic injuries. We hope this knowledge will enhance the clinician’s ability to recognize situations in which injuries of the PCL should be suspected, and aid in an accurate and timely diagnosis.

Patients and methods Between 1993 and 1999, 587 patients with acute and chronic PCL-deficient knees were seen at our institution. The diagnosis was made using a detailed history in connection with a thorough physical examination and posterior stress-radiographs. To diagnose PCL insufficiency, the posterior drawer test and the posterior sag test were done. Assessment of the posterolateral corner was made with the external rotation test at 30° and 90° degrees of knee flexion and the posterolateral drawer test [3, 31]. General inclusion criteria for the study included a PCL tear confirmed by clinical examination and stress-radiography. A side-to-side difference (SSD) of posterior tibial displacement of ≥5 mm on posterior stress-radiographs in 90° of flexion was considered diagnostic for a PCL tear according to the amount of laxity on posterior drawer testing [23]. At initial presentation all patients had bilateral posterior stressradiographs taken in 90° of knee flexion with an applied force of 15 kp using the Telos device (Telos, Marburg, Germany) (Fig. 1). The patient lies in the lateral decubitus position with the involved limb on the table. The limb is positioned in neutral rotation and the load applied to the anterior proximal tibia at the level of the tibial tubercle. A lateral radiograph is taken with the knee flexed approximately 90°. The lateral radiograph is taken from medial to lateral with a standard tube-to-cassette distance of 1.15 m. Radio-

Fig. 2 Posterior tibial displacement of 22 mm on stress-radiograph (90° of flexion)

graphs were performed only by experienced orthopaedic radiologic technicians. The stress-radiographs were evaluated according to the technique described by Jacobsen [15]. After establishing a tibia plateau line, perpendicular lines tangential to the most posterior aspects of the medial and lateral tibial plateaux and the femoral condyles were drawn. With rotation of the limb, the midpoint between the two corresponding lines was established, and these landmarks were then used to measure skeletal displacement of the knee (Fig. 2) [16]. Patients who had MRI images that indicated a rupture of the PCL but had a SSD of posterior displacement of less than 5 mm were determined to have partial ruptures and were not included in this study. Of the 587 patients, 494 met the inclusion criteria and formed the study group. Patients were further subdivided into groups concerning the duration of PCL insufficiency. The following groups were defined, based on the time between injury and first visit at our institution (Table 1). Furthermore, we differentiated between an isolated PCL lesion versus a combined posterior instability pattern. To define these subgroups, a SSD of 5–12 mm of posterior tibial displacement on stress-radiographs was classified as an isolated injury, whereas a displacement of more than 12 mm was considered to be a combined injury [11]. For statistical analysis the chi-square test, the Mann-Whitney U Wilcoxon rank sum test, and the Kruskal-Wallis H test for independent values was used. The significance level was set at p<0.05.

Table 1 Patient groups with respect to the duration of posterior cruciate ligament (PCL) insufficiency Group I Group II Group III Group IV Fig. 1 Posterior stress-radiography in 90° of flexion using the Telos device with an applied load of 15 kp

Acute Subacute Short-term chronic Long-term chronic

≤30 days 31 days–1 year 1–5 years >5 years

(n=54) (n=199) (n=119) (n=122)

188 Table 2 Demographic data and causes of injury in the patient groups All patients (n=494)

Group I <30 days (n=54)

Group II <1 year (n=199)

Group III 1–5 years (n=119)

Group IV >5 years (n=122)

Time between injury and first visit (months) Age at time of injury (years) Male/female (percent)

44.4±68.6 27.5±9.9 392/102 (79.4/20.6)

0.45±0.3 28.9±8.3 47/7 (87.0/13.0)

4.9±2.8 29.8±10.4 168/31 (84.4/15.6)

30.1±13.3 28.6±9.9 85/34 (71.4/28.6)

142.1±75.6 22.2±7.5 92/30 (75.4/24.6)

Injury mechanisms: Traffic accident Athletic injury Other Unknown

224 (45.3%) 197 (39.9%) 59 (11.9%) 14 (2.8%)

11 (20.4%) 37 (68.5%) 5 (9.3%) 1 (1.9%)

82 (41.2%) 83 (41.7%) 30 (15.1%) 4 (2.0%)

57 (47.9%) 42 (35.3%) 16 (13.4%) 4 (3.4%)

74 (60.7%) 35 (28.7%) 8 (6.6%) 5 (4.1%)

Results Demographic data and injury causes Demographic patient data of the study cohort and of the groups are shown in Table 2. When first presenting to our institution, the mean duration of PCL insufficiency was 44.4±68.6 months. Some 54 (10.3%) patients were seen within 30 days after injury. Another 199 (40.3%) patients presented within the first year after injury. Almost half of the patients were seen more than 1 year after injury. The mean age at the time of injury was 27.5±9.9 years, with 44% of the patients in the age group of 20–30 years. Patients who presented more than 5 years after injury (n=122, group IV) had a mean age of 22.2±7.5 years and were significantly younger than patients of other subgroups (p<0.0001). Furthermore, 392 (79.4%) patients were male, 102 (20.6%) female. The sex ratio was not different in the four groups. Vehicular trauma (45.3%) and injury from sporting activities (39.9%) were the main causes of PCL lesions. The remaining 12% resulted from other activities. While sports injuries predominated in patients presenting in the acute or subacute time period (groups I and II), there was a significantly higher incidence of vehicular trauma (p<0.0001)

Fig. 3 Causes of injury in the study cohort (n=494)

in the patients with chronic PCL insufficiency (groups III and IV). A detailed analysis of the causes of injury is given in Fig. 3. Motorcycle accidents were the most frequent cause, accounting for 28.1% of all cases. Soccer injuries accounted for 24.7%, with 18% of all soccer injuries affecting the goalkeeper. Injury mechanisms Among all 494 patients 244 (49.4%) were able to give additional information about the injury mechanism. They could describe the exact position of the foot/leg and the acting force when the injury happened. The most commonly reported mechanisms were ‘dashboard injuries’ (38.5%) and falls on the flexed knee with the foot in plantar flexion (24.6%). The incidence of the different injury mechanisms is given in Fig. 4. Stress radiography The mean posterior displacement on stress-radiographs (90° of flexion) was 13.4±4.7 mm.There was no significant difference in the groups. Some 232 (47%) patients had a posterior displacement of 5–12 mm and were classified as isolated PCL ruptures. There were 262 (53%) pa-

Fig. 4 Specific injury mechanisms (n=244)

189 Table 3 Posterior tibial displacement (SSD); ratio of isolated/combined PCL injuries of the study groups All patients

Posterior displacement (SSD) ±SD (mm) Range (mm) Isolated PCL lesion/combined posterior instability (percent)

(n=494)

Group I <30 days (n=54)

Group II <1 year (n=199)

Group III 1–5 years (n=119)

Group IV >5 years (n=122)

13.4±4.7 (5–30) 232/262 (47.0/53.0)

12.0±4.5 (5–24) 32/22 (59.3/40.7)

13.1±4.5 (5–26) 97/102 (48.7/51.3)

13.1±5.0 (5–30) 62/57 (52.1/47.9)

14.6±4.6 (5–26) 41/81 (33.6/66.4)

Fig. 5 Isolated PCL insufficiency versus combined instability with respect to injury mechanism

tients with a posterior tibial displacement >12 mm who were classified as combined injuries. Patients with a history of PCL insufficiency lasting longer than 5 years showed a significantly higher proportion of combined instabilities compared with the other groups (p=0.004) (Table 3). A combined PCL insufficiency was found in 143 (63.8%) of the 224 patients who were injured in traffic accidents, whereas in athletic injuries combined injuries represented 47.5% (107 of 197) (Fig. 5). This difference was significant (p<0.0001). The mean posterior tibial displacement after vehicular trauma was 14.8±4.9 mm versus 12.4±4.2 mm after athletic injury (p<0.0001).

Discussion The incidence of PCL injuries in the general population has not been clearly defined. The reported incidence of PCL ruptures has varied, with PCL injuries representing between 1% and 44% of all knee ligament injuries in various studies [7, 8, 14, 20, 30]. In a prospective study in a trauma population, Fanelli reported the incidence to be 38% in patients with an acute haemarthrosis of the knee joint. Of these patients 56.5% were injured in traffic accidents, 32.9% were athletic injuries [7, 8]. In the North American National Football League approximately 2% of professional players have demonstrated signs of PCL instability [1]. However, the overall incidence of PCL injuries in an athletic population has not been evaluated to date [12]. To our knowledge no study has evaluated the

epidemiology of PCL injuries in a large patient population. In our patient population, PCL lesions primarily occurred in young adults, with a mean age of 27.5 years at the time of injury. More than 40% of patients were between 20 and 30 years of age. Surprisingly, patients with a history of more than 5 years of PCL insufficiency were significantly younger at the time of injury (22.2 years) compared witho the other groups. The age distribution of the patient population is important with regard to the natural history of PCL insufficiency, which has been a matter of debate. Several reports have challenged the assumption that patients with isolated injury do well when treated conservatively [18, 28, 30]. Numerous studies indicate a gradual deterioration of knee function with increasing time from injury due to the occurrence of degenerative arthritis, mainly in the medial compartment and the patellofemoral joint [5, 10, 18, 29, 30]. These findings should be taken into account when deciding between surgical or conservative treatment, especially in younger patients. Previous studies have shown that most injuries to the PCL occur in one of two settings, a motor vehicle accident or an athletic injury [2, 8, 22, 23]. According to Clancy and Sutherland, vehicular trauma accounted for approximately 50%, sporting activities approximately 40% and other activities approximately 10% of all PCL injuries [2]. This is consistent with our results: 45% of patients were injured in a motor vehicle accident, and 40% were injured during athletic activity. Other activities (working/recreational accidents) accounted for 12% of all injury mechanisms and played only a minor role. We identified two specific injury causes. Motorcycle accidents (28.1%) and soccer injuries (24.7%) were by far the most common specific injury causes, together representing over 50% of all our PCL ruptures. In soccer, the goalkeeper in particular is at increased risk for sustaining a PCL rupture due to the greater chance of sustaining an anterior blow from another oncoming player. More than 18% of all soccer-related ruptures affected the goalkeeper. These findings support the thesis that the incidence of PCL injuries is highly sport-specific [12]. In our patient population almost 80% of the PCL injuries occurred in men; playing soccer and riding a motorcycle were the two main causes of injury in our patients, and these are often more male-oriented activities. The primary causes of injury varied greatly between the acute and chronic PCL deficiencies. In patients diagnosed during the acute phase (within 30 days of injury),

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nearly 70% were injured in athletic activities. In contrast, more than 60% of patients with a long-term chronic PCL insufficiency had been injured in a motor vehicle accident. Patients injured in high-energy motor vehicle accidents suffer a higher incidence of additional life-threatening injuries, and ligamentous knee injuries can be easily overlooked. Nevertheless, it is crucial to assess the possibility of a knee injury in these patients as well. In the acute setting of a suspected PCL rupture, the mechanism of injury is the most important information to be obtained. The circumstances in which the knee injury was sustained affects the risk of associated injuries and helps to distinguish between an isolated versus a combined multiligamentous derangement of the knee [1]. Almost half of the patients of the study population were able to give detailed information with respect to the injury mechanism. The most common injury mechanism was a ‘dashboard injury/anterior tibial blow injury’ (38.5%). In this setting the knee is in a flexed position and a posteriorly directed force is applied to the proximal tibia as the knee strikes the dashboard [1]. An injury of the PCL may easily happen under these circumstances, because the PCL is the primary restraint to straight posterior translation of the tibia at most positions of knee flexion [11, 20, 21]. With the knee in external rotation, the traumatic forces are directed toward the posterolateral and lateral structures of the joint [1, 21]. The second most common injury mechanism was a fall on the flexed knee with the foot in plantar flexion (24.6%). In this setting the site of impact is the tibial tubercle, and the proximal tibia is driven posteriorly relative to the femur. Another mechanism for PCL injury is a sudden violent hyperextension of the knee joint; this accounted for 11.9% of all our injury mechanisms. This mechanism may result in disruption of the posterior capsule as well [1]. In summary, knees injured via high-energy trauma should be very carefully evaluated to rule out combined ligament injuries, which are more common in this setting [1, 21, 29]. Although a PCL rupture can be reliably diagnosed with a thorough, precise physical examination and a detailed patient history [21], the diagnosis is often not made until long after the injury [14]. Isolated PCL tears in particular may be missed in the acute setting, either because patients are unaware of the injury [30], or because they present with unspecific symptoms and lack subjective instability [12, 22, 23]. With the typical injury mechanisms known, the key for reliably detecting these lesions in the acute setting is a high index of suspicion fro the primary treating physician. A weakness of our study is a possibly biased patient population. As a tertiary referral centre, most of the presenting patients were symptomatic. In a prospective study Shelbourne et al. showed that patients with a chronic isolated PCL injury are less symptomatic than patients with chronic ACL deficiencies [30], and it is not known how many PCL patients do not seek medical advice because they suffer only subtle symptoms. PCL injuries may be classified with respect to timing (acute versus chronic) and severity of injury (isolated or

combined), and both variables directly affect the treatment and prognosis [2, 12, 30]. The incidence of isolated vs combined PCL injuries varies with respect to the patient study population. In an athletic patient population, isolated PCL ruptures predominate, whereas in high-energy injuries most ruptures are of the combined type [12]. These findings are easily explained with higher forces acting on the knee joint in high-velocity injuries [8, 14]. In most previous reports the diagnosis of PCL injury and grading of posterior laxity was made on the basis of the clinical examination. While it has already been demonstrated that stress-radiography is superior to a clinical examination or arthrometer measurements when trying to determine the functional status of the PCL [13], assessment of the posterolateral structures of the knee and quantification of external tibial rotation remains difficult [24, 31]. On the other hand, numerous selective dissection studies on cadaver knees have shown that after isolated sectioning of the PCL, posterior tibial displacement does not exceed 12 mm [11, 12, 25, 31]. Based on these data we differentiated between isolated and combined injuries according to the posterior tibial displacement values found on the stress-radiographs. With these guidelines, we found the incidence of combined posterior instabilities to be 53% (262 patients). The remaining 232 patients (47%) with a posterior displacement ≤12 mm were classified as isolated PCL tears. This is in line with data reported by Clancy and Sutherland. In a survey of 191 patients, they found approximately 40% of the PCL injuries to be isolated and approximately 50% to be combined. Combined ACL/PCL injuries and posterolateral corner injuries were the most common combined injury types [2]. In our experience the vast majority of combined posterior instabilities involve the posterolateral structures of the knee. This is supported by several biomechanical studies, which have demonstrated strong functional interactions of the PCL and the posterolateral structures of the knee in providing posterior stability of the knee joint [12, 24, 31]. We found significantly more combined lesions in high-velocity injuries (64%) compared with athletic injuries (46%). The mean posterior displacement on posterior stress-radiographs was 13.4 mm (SSD) for the entire study population. Patients with athletic injuries had a mean posterior displacement of 12.4 mm (SSD) compared with 14.8 mm (SSD) after vehicular trauma. Patients with a history of PCL insufficiency of more than 5 years showed a significantly increased posterior tibial displacement compared with the other groups. It is not known if this is related to the high proportion of high-velocity injuries in this group, or if there is a gradual slackening of the secondary stabilizers of posterior tibial displacement. Conclusions: 1. Injuries of the PCL primarily occur in two different settings: 45% of patients were injured during vehicular trauma, and 40% were athletic injuries. Motorcycle ac-

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cidents and soccer injuries are the most common specific causes of injury. Dashboard injuries and falls on the flexed knee represent the most common injury mechanisms. 2. Based on the present findings, the diagnosis and treatment of PCL injuries are often delayed despite typical injury mechanisms and symptoms. A detailed history in connection with a thorough clinical examination is crucial in establishing the correct diagnosis in the acute setting. 3. Stress-radiography in 90° of flexion is a useful adjunct to quantify posterior tibial displacement and allows for differentiation between isolated PCL lesions and combined posterior instabilities. 4. Combined PCL instabilities were present in 53% of patients, with a significantly higher incidence after vehicular trauma (64%) compared with athletic injuries (46%). It is crucial to distinguish between isolated PCL and combined PCL instabilities in order to optimise the therapy regimen and the prognosis of the injury. Acknowledgement We acknowledge the help of Petra Broschinsky for data acquisition.

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