Posteromedial Knee Capsule Tear Without Concomitant Ligament Rupture or Meniscal Pathology in a Pediatric Athlete

ABSTRACT

The posterior knee capsule is a critical structure for tibiofemoral stability, limiting hyperextension, and posterior translation. Injuries to this structure are rare and typically occur alongside anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) tears. To date, no cases have been reported of a posteromedial capsule tear without concomitant ligamentous rupture or meniscal injury, leaving its clinical significance and optimal management unclear. We report on a 15‐year‐old male who sustained a hyperextension knee injury while playing basketball, presenting with pain and an abnormal gait. Diagnostic arthroscopy revealed an intact ACL and a full‐thickness 3 cm posterior capsule tear, which was repaired arthroscopically. At 6 months postoperative, mild recurvatum persisted. This case parallels ramp lesions, another posteromedial injury with, at times, conflicting management guidelines. This case underscores the need for further research into the diagnosis, management, and long‐term outcomes of posterior capsule injuries given that they are poorly understood in isolation due to their frequent association with multi‐ligamentous trauma. Future studies should aim to evaluate best practice and determine whether surgical intervention is necessary or if conservative management could yield comparable results.

Key Clinical Message

Posterior knee capsule tears can occur in isolation without concomitant ligament or meniscal injury and residual hyperextension may remain postoperative repair. This case demonstrates the diagnostic challenges and management of an isolated posterior capsule tear while calling for further research to determine best practice for this rare but clinically relevant injury.

1. Introduction

The knee capsule is a multilayered structure composed of an outer fibrous layer and an inner synovial membrane that secretes fluid for joint lubrication. The capsule surrounds the knee joint as a continuous sheet, with regional thickenings at ligaments [1]. Among its components, the posterior capsule plays a crucial role in stabilizing the tibiofemoral joint by limiting posterior translation and hyperextension forces [2]. With its structural continuity, injuries to the posterior capsule almost always occur in conjunction with meniscal lesions or extensive multi‐ligamentous injuries, such as anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) tears [2, 3]. To date, no cases have been documented in the literature describing a posteromedial capsule tear without associated ligamentous rupture or meniscal damage, making its clinical relevance and optimal management unclear [3].

A comparable injury with better‐established significance is the ramp lesion, which involves the posterior horn of the medial meniscus. Ramp lesions have been well described and shown to affect knee stability if left untreated [4]. Whether this instability occurs with injury to the posteromedial capsule of the knee remains unexplored [5].

This case report presents a posteromedial capsule tear discovered during diagnostic arthroscopy, without clinically significant injury to adjacent structures, in a patient with prolonged knee pain after a hyperextension injury. Given the gap in literature describing management and implications of isolated posterior capsule tears, a parallel is drawn between this injury and the better‐established ramp lesion. In all, this report raises important clinical questions regarding the diagnosis, functional implications, and treatment of posterior capsule injuries, particularly whether surgical intervention is warranted or if conservative management may suffice.

This is a single‐patient case report and does not constitute human subjects research as defined by federal regulations, as it does not involve a systematic investigation designed to contribute to generalizable knowledge. Accordingly, Institutional Review Board approval was not required per institutional guidelines; however, written informed consent was obtained from the patient's legal guardian for publication of the clinical details and accompanying images.

2. Case Presentation

A 15‐year‐old male presented to the emergency department with acute left knee pain following a hyperextension injury sustained while playing basketball. He described a sudden buckling sensation after forcefully planting his left foot. The patient was discharged from the emergency department with crutches and a brace for suspected patellar fracture.

He was seen and evaluated in the orthopedic sports medicine clinic the following day accompanied by his mother. In addition to the above history, the patient reported he had been dealing with left knee pain for 2 months prior to this injury but had not been evaluated.

On physical examination, the patient demonstrated an antalgic, quadriceps avoidance gait. Effusion of the left knee was seen without erythema or bruising. The range of motion of the joint was −20°–40°. Despite significant guarding, special testing of the knee including: anterior drawer, posterior drawer, Lachman, varus, and valgus was normal.

The X‐ray performed at the hospital was read as an avulsed fracture fragment arising from the lateral patellar facet with possible joint effusion. Independent interpretation by the orthopedic surgeon in the clinic determined this was instead a bipartite left patella, without fracture (Figure 1). MRI studies revealed an acute high‐grade sprain of the ACL with partial‐thickness tears in the midsubstance and at the femoral origin. Of note, no full‐thickness tear of the ACL was identified; however, the radiologist noted the possibility of a functional full‐thickness tear. In addition, a Grade 2 sprain of the fibular collateral ligament, a Grade 1–2 sprain of the medial collateral ligament, and a bipartite patellar configuration were identified. As well as a large effusion in the posteromedial aspect of the knee on axial view. Overall, concerning for a posterior capsule strain (Figure 2).

FIGURE 1.

Preoperative radiographs. Standing anteroposterior view of the bilateral knees (A). Axial (sunrise) view demonstrating a superolateral bipartite patella, initially interpreted as an avulsion fracture (B). Lateral radiograph demonstrating preserved alignment and joint effusion without acute fracture (C).

FIGURE 2.

Preoperative MRI. Sagittal non‐fat‐suppressed MRI showing preserved continuity of the anterior cruciate ligament (ACL) (A). Sagittal T2‐weighted fat‐suppressed MRI demonstrating increased intrasubstance signal and fiber irregularity within the ACL (B). Axial T2‐weighted fat‐suppressed MRI demonstrating a large effusion (C).

Diagnosis was complicated by significant guarding in office, limiting physical examination, as well as an equivocal interpretation of the anterior cruciate ligament via MRI studies. The orthopedic surgeon discussed operative and nonoperative treatment options with the patient and his mother. The nonoperative treatment plan involved rest, bracing, physical therapy, and a plan to follow up in office to evaluate any residual instability with the possibility of intervention later. Alternatively, examination under anesthesia and diagnostic arthroscopy with possible ACL reconstruction was offered, given the acute exacerbation of pain following hyperextension injury, and concern for ACL injury that could not be definitively characterized through imaging and physical examination alone. The risks and benefits of each route were discussed at length with both the patient and his mother. Driven by his motivation for a rapid return to play as a competitive athlete, the patient and his mother ultimately elected to undergo diagnostic arthroscopy of the patient's left knee over an attempt at conservative management.

3. Methods

Examination under anesthesia and diagnostic arthroscopy was performed 3 weeks after the injury. The examination demonstrated no evidence of ligamentous laxity. Despite MRI signal changes suggesting partial ligament sprain, no biomechanically significant ligament insufficiency was present on examination under anesthesia. Both the anterior and posterior drawer tests, pivot shift, as well as the Lachman test were stable, indicating intact cruciate ligaments. Varus and valgus stress testing showed no medial or lateral gapping, and McMurray's test was negative, overall suggesting no collateral ligament or meniscal pathology, respectively.

Arthroscopic evaluation revealed a frayed but structurally intact ACL, with no empty notch sign. The ACL was debrided of superficial degenerative tissue to restore a smooth surface (Figure 3). PCL, collateral ligaments, menisci, and articular surfaces were intact. Visualization of the posteromedial compartment was enhanced using the Gillquist maneuver, allowing for complete assessment of the posterior structures. This revealed a full‐thickness horizontal tear measuring approximately 3 cm within the posterior capsule. The tear was located about 2.5 cm proximal to the medial meniscus and was clearly distinct from the typical posteromedial location of a ramp lesion (Figure 4A).

FIGURE 3.

Arthroscopic evaluation of the ACL. Intact femoral attachment and preserved ACL fiber continuity with mild fraying (A). Arthroscopic view following debridement of superficial tissue, demonstrating a smooth, structurally intact ACL (B).

FIGURE 4.

Arthroscopic visualization of the posteromedial capsular tear. Full‐thickness horizontal tear of the posteromedial capsule measuring approximately 3 cm (A). Arthroscopic view during repair demonstrating suture passage through the capsular tissue (B).

Prior to arthroscopy, the initial working diagnosis included an ACL injury, with concomitant injury to the collateral ligaments, given the hyperextension mechanism, reported buckling sensation, and imaging. Meniscal pathology, particularly a ramp lesion, was also considered, as were osteochondral injury and bone contusion.

These possibilities were systematically excluded during intraoperative assessment, as a stable examination under anesthesia and arthroscopic visualization confirmed functionally and structurally intact PCL, menisci, and collateral ligaments (Table 1). In addition, the ACL was functionally intact on examination, and while frayed, it was structurally intact and without tear on gross examination. A full‐thickness tear of the posterior capsule was revealed and in the absence of other pathology represented the only structural abnormality requiring surgical intervention (Figure 4A).

TABLE 1.

Differential diagnostic framework.

Injured structure	History		Physical examination		Imaging (MRI)	Diagnostic arthroscopy		Differential diagnosis
	Typical findings	Patient	Typical findings	Patient	Patient	Examination under anesthesia (EUA)	Gross appearance	Preoperative	Postoperative
ACL	“pop” heard buckling “gave way” pivoting, cutting, jumping, immediate effusion Hyperextension [6, 7]	✓buckling ✓immediate effusion ✓hyperextension	Anterior drawer test, Lachman test, pivot‐shift, quadriceps avoidance gait [6]	✓quadriceps avoidance gait ✗anterior drawer ✗Lachman ✗pivot‐shift	✓ Acute high‐grade sprain indicating partial‐thickness or functional full‐thickness tear	✗anterior drawer ✗Lachman ✗pivot‐shift	Frayed, but structurally intact after debridement	High suspicion	Ruled out by EUA and arthroscopy
PCL	“pop” heard immediate effusion Buckling “gave way,” Hyperflexionhyperextension fall onto flexed knee [8]	✓buckling ✓immediate effusion ✓hyperextension	Posterior drawer test Posterior sag test [8]	✗posterior drawer Posterior sag not assessed	✗ Negative on preoperative studies	✗posterior drawer Posterior sag not assessed	Structurally intact	Low suspicion	Ruled out by EUA and arthroscopy
MCL	Direct valgus blow Localized effusion (medial) hyperextension [9]	✓localized medial effusion ✓hyperextension	Valgus test [9]	✗valgus test	✓Grade 1–2 sprain	✗valgus test	Structurally intact	Moderate suspicion	Ruled out by EUA and arthroscopy
LCL	Direct varus blow Localized effusion (lateral) hyperextension [10]	✓hyperextension	Varus test [10]	✗varus test	✓Grade 2 sprain	✗varus test	Structurally intact	Moderate suspicion	Ruled out by EUA and arthroscopy
Menisci	Twisting, cutting, pivoting on planted foot, delayed effusion [11]	✓Planted foot	McMurray's, Apley's [11]	✗McMurray's Apley's not assessed	✗ Negative on preoperative studies	✗McMurray's Apley's not assessed	Structurally intact	Moderate suspicion	Ruled out by EUA and arthroscopy

Note: Typical diagnostic features of suspected knee injuries compared with findings in the present case (bolded).

The posterior capsule tear was managed arthroscopically with a 70‐degree arthroscope used to optimize visualization of the posteromedial compartment, and a dedicated portal was established to access the lesion. Sutures were passed through the posterior, inferior, and superior capsule to approximate the tissue edges and achieve stable closure of the defect (Figure 4B). Bone marrow venting was used in the notch anterior to the ACL to promote healing.

4. Results

Postoperatively, the patient was immobilized in a knee brace for 6 weeks and allowed weight‐bearing as tolerated. Progress in rehabilitation was initially limited by kinesiophobia, but gradual improvements in motion and function were achieved. A subsequent slip‐and‐fall incident at home, 9 weeks postoperative, prompted repeat imaging, which confirmed an intact posterior capsule repair, interval improved appearance of the anterior cruciate ligament, and preserved menisci (Figure 5).

FIGURE 5.

Postoperative MRI 9 weeks after repair. Sagittal non‐fat‐suppressed MRI demonstrating preserved continuity of the ACL with improved structural appearance compared to preoperative imaging (A). Sagittal T2‐weighted fat‐suppressed MRI demonstrating an intact posteromedial capsule repair without evidence of re‐tear, with preserved meniscal integrity and interval improvement of ACL edema (B).

Following this event, he resumed rehabilitation and continued progressing toward full, unrestricted athletic participation. By 15 weeks, the patient was participating in formal physical therapy and reported only occasional anterior knee pain during running. At 6 months, the patient demonstrated stable knee function, although mild recurvatum persisted on examination. At this visit he was cleared to return to basketball without a brace as tolerated. The patient went on to play summer basketball with some mild pain.

At 8 months postoperative, the patient's reported Lower Extremity Functional Scale (LEFS) was 79/80, improved from 16/80 upon initial visit. The patient was discharged to a home exercise physical therapy program at this time. At 1 year postoperative, the patient had no complaints of left knee pain. However, due to reported shin splints, the patient ultimately did not return to basketball for the regular season. The following spring, he went on to run track.

5. Discussion

To the authors' knowledge, this is the first reported case of a full‐thickness tear of the posteromedial knee capsule in the absence of concomitant ligamentous rupture or meniscal pathology [2, 3, 12]. Injuries to the posterior capsule are rare and typically occur alongside other ligamentous injuries due to the structurally continuous nature with surrounding ligaments of the posteromedial and posterolateral corners, shared load distribution with the ACL and PCL against hyperextension, and thus, common mechanism of injury [2, 3, 13]. In ACL‐associated injuries, fluid typically remains within the posterior capsule, but edema or hematoma may displace it [2]. Given the PCL's role in limiting posterior tibial translation, injuries to the PCL often co‐occur with damage to structures such as the posterolateral capsule, medial collateral ligament, or posterior oblique ligament [14]. The gold standard for identification is MRI, where posterior capsule disruption appears as hyperintensity on T2‐weighted sequences. These tears can involve the posteromedial or posterolateral corners of the knee, although normal openings for vasculature and nerves in the intercondylar region must not be mistaken for pathology. In chronic cases, the capsule may appear thickened and hypointense [2].

Despite limited literature describing tears of the posterior capsule without clinically significant concomitant ligamentous or meniscal injury, emerging studies on biomechanics have suggested this to be a plausible injury pattern [2, 13]. A recent cadaver study by Noyes et al. investigated the functional relationship between the posterior capsule and cruciate ligaments in resisting hyperextension and found that among these structures, the posteromedial capsule produced the greatest median resisting force to knee hyperextension independently. In the study, the entirety of the posterior capsule provided 54.7% of the total resistance to hyperextension, compared to the cruciate ligaments combined 25.3% [13]. This is supported by several studies that have found greater increases in knee hyperextension with failure of the posterior capsule versus isolated failure of the cruciate ligaments [2, 15]. Limited studies have investigated the sequence of failure of the structures involved in resisting knee hyperextension. A cadaver study by Bizot et al. utilized progressive passive hyperextension and found that the posterior capsule was the first structure to fail, with the PCL ultimately failing as well. However, no ACL rupture was noted in this sample before dislocation [16]. A more recent cadaver study by Fornalski et al. evaluated posthyperextension injury at 15° and 30° and corroborated the posterior capsule failing first, followed by the ACL with greater degrees of hyperextension. However, no gross PCL rupture was observed [17]. While the sequence of cruciate failure is unclear, the commonality is posterior capsule failure prior to cruciate failure in hyperextension injury. Together, this suggests that the posterior capsule acts as both the initial and major restraint to hyperextension [13, 15, 16, 17]. With this, hyperextension injuries may occur in which the force causes posterior capsule failure, with preservation of the cruciate ligaments' integrity, likely depending on magnitude. Thus, providing a plausible biomechanical explanation for the injury pattern seen in this case. Biomechanically feasible outside of a multiligamentous context, the gap in the current literature on posterior capsule tears in isolation may be due to true rarity, as well as insufficient detection and subsequent underreporting. Lack of specificity in clinical testing for injury of the posterior capsule may be one barrier to detection [18]. This was observed in our case as special testing of the knee, both in clinic and under anesthesia, was normal despite the full‐thickness tear of the posterior capsule confirmed by arthroscopy. This included: anterior drawer, posterior drawer, Lachman, varus, and valgus testing. In addition, minimal clinical laxity produced when the posterior capsule is the sole disruption may contribute to underdetection as well [19].

In our case, although MRI demonstrated a possible partial‐thickness tear of the ACL as well as sprains of the collateral ligaments, stable examination under anesthesia confirmed that these structures were functionally intact. In addition, arthroscopy confirmed that the full‐thickness tear of the posterior capsule was the sole clinically relevant structural lesion, with the PCL, collateral ligaments, and menisci intact (Table 1). On arthroscopy, the ACL was frayed but structurally intact and without tear on gross examination. Debridement and bone marrow venting was performed for the ACL, and its appearance on MRI improved postoperatively (Figure 5). Despite radiology read of ACL sprain, the novelty of this case remains. Given that the current literature situates posteromedial capsule tear repair in the context of complete ACL tears or other significant multiligament knee injuries whereas ACL fibers were intact in the present case [2, 3, 20].

The current literature strongly supports repairing posterior capsule tears when discovered in multiligamentous injury. Repair is particularly recommended in the context of concomitant cruciate ligament tears, as neglecting the posterior capsule may lead to later failure of cruciate ligament reconstructions [20, 21]. Given the typical multiligamentous presentation, there is a lack of consensus regarding the significance and management of posterior capsule tears when they present as the sole clinically relevant lesion [21]. Some tears may heal with conservative management alone or eventually require surgical intervention, depending on the severity [20, 21]. A technical note by Ahn et al. described the management of an acute tear of the posterolateral knee capsule in a chronic PCL injury. Ahn et al. referred to this as an isolated posterolateral knee tear given that the PCL was lax but healed from initial injury 2 years prior to presentation. In this case, PCL reconstruction was performed, and a posterior trans‐septal portal was used for arthroscopic management of the posterolateral capsule. Postoperatively, the patient was followed for 4 years and had no posterior or posterolateral instability. Despite this positive outcome, the authors noted that this approach may not yield similar results in cases of posteromedial capsule tear, given that medial instability persisted when this technique was applied to a separate case of posteromedial capsule tear with ACL and medial collateral involvement. However, Ahn et al. maintained that all tears of the posterior capsule should be addressed if found [12]. With this gap in knowledge, the efficacy of surgical management of posteromedial capsule tears remains unknown. In addition, the potential stability and functional deficits from leaving these injuries untreated is undefined [5]. In our case, diagnostic arthroscopy was elected over conservative nonoperative treatment given the patient's strong motivation to return to play and acute injury. The decision to repair the posterior capsule was made intraoperatively based on concerns regarding potential instability and functional impairment due to the full‐thickness tear [5]. Despite repair, the patient continued to demonstrate mild recurvatum, raising important questions about whether the residual symptoms stem from the injury itself, the surgical repair, or a potentially missed concomitant injury.

A useful parallel can be drawn between posterior capsule injuries and ramp lesions. While the full‐thickness posterior capsule tear identified in this case did not involve the meniscus and was substantially proximal to the typical location of a ramp lesion, both involve posteromedial structures that may influence knee stability. Ramp lesions are present in 9%–17% of ACL tears and may contribute to residual instability even after reconstruction [4, 22]. Specifically, increased anterior tibial translation and rotational instability are observed in untreated ramp lesions, highlighting the importance of the posteromedial soft tissue restraints in maintaining knee stability [5]. Despite this, there is still no universal agreement on the need for surgical repair of ramp lesions, particularly for smaller, stable tears that may heal nonoperatively [23]. This ambiguity mirrors the lack of clarity surrounding the clinical impact and treatment of isolated posterior capsule tears. Both injuries involve secondary stabilizing structures of the knee, particularly in resisting excessive tibiofemoral translation. Considering the posterior capsule's significant role in preventing hyperextension, it is plausible that an untreated tear could result in similar instability to that of the ramp lesion, persistent pain, and altered biomechanics [4, 5, 23, 24]. However, conclusions on the true functional implications of untreated posterior capsule injuries remain to be studied.

This case report is limited by its single‐patient design, which restricts the generalizability of conclusions regarding the efficacy of surgical repair. In addition, due to the arthroscopic nature of the procedure and the intimate anatomic relationship between the posterior capsule and adjacent posteromedial corner structures, the precise contribution of capsuloligamentous structures, such as the posterior oblique ligament, could not be definitively determined. Consequently, the lesion is appropriately described throughout as a tear of the posteromedial capsule. Though the patient reported functional improvement, persistent recurvatum seen in subsequent follow‐up raises the possibility of an undetected concomitant injury or incomplete healing in this case. In addition, postoperative recurvatum introduces uncertainty about the durability of repair and long‐term stability. Further, the use of bone marrow venting in this case, while biologically promising for healing, has not been systematically studied for posterior capsule injuries. Existing data on its benefits in meniscal repair suggests potential value but requires further investigation in the context of injuries to the posteromedial capsule [25]. Randomized trials comparing surgical and conservative management are essential to guide treatment decisions and develop evidence‐based protocols for posterior capsule tears. Further research in these areas, as well as clinician awareness of isolated posterior capsule injury without concomitant ligamentous injury as an entity, may help improve detection and outcomes in isolated posterior capsule tears.

This case highlights the rarity of posterior capsule injury without concomitant ligamentous rupture or meniscus pathology. Rarity and potential underdetection have contributed to the current uncertainty surrounding posterior capsule tears as a principal lesion. While the posterior capsule is known to contribute to knee stability, its isolated disruption remains poorly characterized due to its frequent association with multi‐ligamentous trauma. Concerns over potential instability and functional limitations drove the decision to surgically repair the capsule in this case. However, the persistence of recurvatum postoperatively raises important questions about the role of the injury itself, the efficacy of repair, and the possibility of missed concurrent injuries. Greater awareness and further research are needed to define the clinical significance of posterior capsule injuries and their management.

Author Contributions

Arianna Paa: project administration, visualization, writing – original draft, writing – review and editing. Doyle Ford: project administration, writing – original draft, writing – review and editing. Faris Jafri: conceptualization, writing – original draft, writing – review and editing. Kareem Siada: writing – original draft. Keith Sims: writing – original draft. Micah Lissy: conceptualization, investigation, methodology, supervision.

Funding

The authors have nothing to report.

Ethics Statement

Institutional review board approval was not required for this case report in accordance with local and national guidelines.

Consent

Written informed consent was obtained from the patient's legal guardian for publication of this case report and accompanying images.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data supporting the findings of this case report are contained within the article. No additional datasets were generated or analyzed.