Partial ACL Tear Treatment: When Surgery Is Needed and When It Isn’t

When a patient receives a diagnosis of a partial ACL tear, the first question is almost always the same: “Does that mean I don’t need surgery?” The honest answer is that it depends. A partial tear is not simply a “minor” version of a complete tear. It’s a distinct clinical entity with its own set of diagnostic challenges, treatment considerations, and long-term implications. At Ochsner-Andrews Sports Medicine Institute in Baton Rouge, Louisiana, Dr. Burnham evaluates partial ACL injuries regularly, and the management decisions are rarely straightforward.

Partial ACL tears account for an estimated 10% to 27% of all ACL injuries (Stone et al., J Am Acad Orthop Surg, 2021). Some patients do well with structured rehabilitation and never require surgery. Others experience progressive instability that eventually leads to a complete rupture, meniscus damage, or cartilage injury. The challenge for the surgeon is identifying which patients fall into which category, and Dr. Burnham’s research on rotatory knee laxity has given us better tools to make that determination.

What Is a Partial ACL Tear?

The ACL is composed of two functional bundles: the anteromedial (AM) bundle and the posterolateral (PL) bundle. A partial tear means one of these bundles is torn while the other remains intact and functional. This is different from a complete tear, where both bundles are disrupted and the ligament can no longer stabilize the knee against anterior translation and rotation.

The distinction matters clinically because a knee with a partially intact ACL behaves differently than a knee with no ACL at all. Patients with partial tears often have some residual stability, particularly during straight-line activities like jogging or cycling. But that residual stability can be deceiving. The knee may feel “almost normal” during everyday life while being functionally insufficient during the cutting, pivoting, and deceleration demands of competitive sport.

Understanding the anatomy of the ACL helps explain why partial tears are so variable in their presentation. The AM bundle is the primary restraint to anterior tibial translation (the classic “Lachman test” motion), while the PL bundle contributes more to rotational stability. A patient with a torn PL bundle and intact AM bundle may have a nearly normal Lachman test but demonstrate subtle rotational instability that only becomes apparent during sport-specific activities or with quantitative testing. This rotational component is also influenced by surrounding structures like the anterolateral ligament complex, which Dr. Burnham has studied extensively.

How Partial ACL Tears Are Diagnosed

Diagnosing a partial ACL tear is one of the more nuanced challenges in sports medicine. The physical examination findings are often subtle. Unlike a complete tear, where the Lachman test and pivot shift are typically positive and unmistakable, a partial tear may present with a soft or delayed endpoint on Lachman testing and a negative or only trace-positive pivot shift. According to the literature, the Lachman test is positive in roughly half of partial ACL tear cases (Pujol et al., Orthop Traumatol Surg Res, 2012).

MRI is helpful but not definitive. Standard MRI can identify a partial tear with reasonable accuracy, but it can also miss them or overestimate the injury. Dr. Burnham has had patients whose MRI suggested an intact ACL but who demonstrated clear rotational instability on examination under anesthesia. Conversely, Dr. Burnham has seen MRI reports describing a “partial tear” in patients whose knees are functionally stable. The imaging is one data point, not the final answer.

The gold standard for confirming a partial ACL tear remains direct arthroscopic visualization. During arthroscopy, the surgeon can probe the ligament, assess the integrity of each bundle individually, and determine whether the remaining tissue provides meaningful stability. This is why Dr. Burnham advises patients that the definitive diagnosis often comes during the procedure itself, and the treatment plan for various scenarios is discussed before going to the operating room.

Rotatory Laxity Exists on a Continuum: What the Research Shows

One of the most important insights guiding the clinical approach to partial ACL tears comes from research Dr. Burnham’s group published in the Journal of Bone and Joint Surgery. In a multicenter study of 354 patients, the study demonstrated that rotatory knee laxity exists on a measurable continuum across ACL injury severity (Lian, Burnham et al., JBJS, 2020).

Using quantitative pivot shift testing with validated image-based software, the study found stepwise increases in lateral compartment translation across three groups: patients with partial ACL tears had the least rotational instability (mean side-to-side difference of 1.4 mm), followed by complete ACL tears (2.5 mm), and then failed ACL reconstructions (3.3 mm). The differences between partial and complete tears were statistically significant (p = 0.02).

What this means for clinical decision-making is significant. A partial ACL tear is not just “less torn” than a complete tear. It produces a measurably different pattern of knee instability. This data helps surgeons counsel patients more precisely: if your partial tear is producing minimal rotational laxity, conservative management may succeed. If the quantitative measures suggest your knee is behaving closer to a complete tear, surgery is likely the better path to protect the meniscus and articular cartilage from the cumulative damage that instability causes over time.

Can a Partial ACL Tear Heal Without Surgery?

Some partial ACL tears can be managed successfully without surgery, but the outcomes are highly dependent on the patient’s activity level, the degree of remaining stability, and the willingness to modify activity demands. This is where honest, individualized conversation matters more than blanket recommendations.

A systematic review of the natural history of non-operated partial ACL tears found that at a mean follow-up of 5.2 years, about 52% of patients returned to sport at their previous level. However, the same review found that pain persisted in 54% of patients and that the pivot shift test, initially negative in all cases, became positive in roughly a quarter of patients over time, suggesting progressive laxity (Pujol et al., 2012). Younger, active patients are at particular risk of progressing to a complete rupture if they attempt to return to cutting and pivoting sports (Stone et al., 2021). Understanding ACL injury risk factors can help guide this decision.

Conservative management typically involves a structured rehabilitation program focused on quadriceps and hamstring strengthening, progressive functional exercises, neuromuscular training, and proprioceptive work. The goal is to build the dynamic muscular stability that compensates for the compromised ligament. For patients who are willing to step back from high-demand sports, or whose daily activities don’t require aggressive pivoting and cutting, this approach can work well.

For the competitive athlete, recreational soccer or basketball player, or weekend warrior who wants to return to unrestricted pivoting activities, the calculus changes. Each episode of giving way risks additional damage to the meniscus and cartilage. These secondary injuries are often what determine the long-term health of the knee, not the ACL tear itself.

When Surgery Is Needed for a Partial ACL Tear

The decision to operate on a partial ACL tear is based on the concept of a “functional” versus “nonfunctional” ACL. A functional partial tear is one where the remaining ligament provides adequate stability for the patient’s activity demands. A nonfunctional partial tear is one where the knee demonstrates clinically meaningful instability despite the partially intact ligament.

Surgical treatment is recommended when one or more of the following factors are present. The patient experiences recurrent episodes of instability or giving way, even with activity modification. The physical examination reveals a positive pivot shift, which indicates rotational instability that rehabilitation alone cannot correct. The patient is a young, active athlete who plans to return to Level I or Level II sports (cutting, pivoting, jumping). There is a concurrent repairable meniscus tear or cartilage lesion that benefits from a stable knee environment. Or the patient has attempted a structured rehabilitation program and continues to experience functional limitations.

Importantly, the presence of a meniscus tear alongside a partial ACL tear often tips the decision toward surgery. A repairable meniscus heals best in a stable knee. If the meniscus is repaired but the partial ACL tear remains nonfunctional, the ongoing instability increases the risk of meniscus re-tear. Protecting the meniscus preserves the long-term health of the knee, and that’s always part of the equation. For more on combined injuries, see the guide on ACL and meniscus tear combined injury treatment.

Surgical Options: Repair, Augmentation, and Reconstruction

When surgery is indicated for a partial ACL tear, there are three main approaches depending on the tissue quality, tear pattern, and timing of presentation: ACL repair, selective single-bundle augmentation, and complete ACL reconstruction.

ACL repair: In select cases, particularly when the tear is acute and the tissue quality is excellent, the torn ACL fibers can be repaired directly rather than replaced. This approach preserves the patient’s native ligament, including its proprioceptive nerve fibers, and avoids the donor-site morbidity associated with graft harvest. Repair is not appropriate for all partial tears, but when the tissue is amenable, it offers a biologically attractive option. Dr. Burnham evaluates the repairability of the ligament arthroscopically before committing to a treatment approach. For patients interested in repair options, the ACL repair with BEAR implant page covers one emerging technology in this space.

Selective single-bundle augmentation: This approach reconstructs only the torn bundle while preserving the intact one. It maintains the remaining bundle’s proprioceptive nerve fibers (which contribute to knee position sense) and protects the blood supply and biological environment of the surviving ligament. Dr. Burnham authored a book chapter on this technique, and when the intact bundle is clearly healthy and functional, augmentation can restore stability while preserving native tissue. A 2022 meta-analysis comparing selective bundle reconstruction to complete ACL reconstruction across 1,107 patients found that the selective approach achieved comparable functional scores and stability outcomes, with a trend toward better anterior laxity measurements on arthrometry (Yeo et al., J Orthop, 2022). A separate meta-analysis from the same year suggested augmentation may produce better functional outcomes (Tegner scores) than complete reconstruction (Bosco et al., J Orthop, 2022).

Complete ACL reconstruction: When the remaining bundle is attenuated, stretched, or structurally compromised, neither repair nor augmentation will provide reliable long-term stability. In these cases, a complete ACL reconstruction is performed, typically using a quad tendon autograft. Dr. Burnham assesses the integrity of the remaining tissue arthroscopically and under direct visualization before committing to any approach. The intraoperative findings, not the preoperative MRI, drive the final surgical decision. A comparison of the available ACL graft options can help patients understand the trade-offs.

The bottom line on surgical approach: the right technique depends on what the surgeon finds in the operating room. Repair is possible when the tissue quality permits it. Augmentation preserves native tissue in select cases. Complete reconstruction remains the standard when the remaining ligament cannot be trusted. All three options produce good outcomes when applied to the right patient, and Dr. Burnham discusses these scenarios with every patient before surgery so the plan is clear regardless of what the arthroscopy reveals.

Recovery and Return to Sport

Whether managed conservatively or surgically, the rehabilitation process for a partial ACL tear follows principles applied at Ochsner-Andrews Sports Medicine to all ACL rehabilitation: restore range of motion, rebuild strength with an emphasis on quadriceps and hip musculature, progressively load the knee through sport-specific patterns, and meet objective criteria before returning to competition. The ACL surgery recovery timeline outlines what to expect at each stage.

For patients who undergo surgery, the recovery timeline is similar to a standard ACL reconstruction, typically 9 to 12 months depending on sport demands and objective testing. The return-to-play criteria require greater than 95% quadriceps symmetry on Biodex isokinetic testing at 60, 180, and 300 degrees per second, greater than 90% hamstring symmetry, greater than 90% hip abduction and external rotation symmetry, and passage of a battery of hop tests at 95% limb symmetry. An ACL-RSI psychological readiness score above 75 is also required before clearing an athlete to return. These criteria are based on published guidelines from Dr. Burnham’s group (Burnham et al., IJSPT, 2026; Hughes, Burnham et al., Orthop J Sports Med, 2019) and reflect the standard of care at Ochsner-Andrews Sports Medicine Institute.

For patients managed conservatively, the timeline is variable. Some patients regain full function within 3 to 4 months. Others reach a plateau where the knee remains symptomatic during high-demand activities, and that’s when the surgical conversation is revisited. Dr. Burnham advises patients upfront: trying conservative management first doesn’t burn any bridges. If it works, great. If it doesn’t, surgery can still proceed with excellent expected outcomes. The functional progression after ACL surgery framework guides the transition from rehab to sport-specific training.

The Bottom Line

Partial ACL tears occupy a gray zone in sports medicine, and that’s precisely why they require careful, individualized evaluation. Not every partial tear needs surgery, but not every partial tear will do well without it. Dr. Burnham’s research has shown that rotatory laxity exists on a measurable continuum, and understanding where a patient falls on that continuum is the key to making the right treatment decision. If you’ve been told you have a partial ACL tear and want a thorough evaluation of your options, contact the office to schedule a consultation with Dr. Burnham’s ACL program in Baton Rouge. The practice sees patients from across Louisiana, including Baton Rouge, New Orleans, Lafayette, Hammond, and the surrounding Gulf South region.

References

• Lian J, Diermeier T, Meghpara M, Popchak A, Smith CN, Kuroda R, Zaffagnini S, Samuelsson K, Karlsson J, Irrgang JJ, Musahl V; PIVOT Study Group. Rotatory knee laxity exists on a continuum in anterior cruciate ligament injury. J Bone Joint Surg Am. 2020;102(3):213-220. PMID: 31876642 | DOI: 10.2106/JBJS.19.00502
• Stone AV, Marx S, Conley CW. Management of partial tears of the anterior cruciate ligament: a review of the anatomy, diagnosis, and treatment. J Am Acad Orthop Surg. 2021;29(2):60-70. PMID: 33394613 | DOI: 10.5435/JAAOS-D-20-00242
• Pujol N, Colombet P, Cucurulo T, et al; French Arthroscopy Society. Natural history of partial anterior cruciate ligament tears: a systematic literature review. Orthop Traumatol Surg Res. 2012;98(8 Suppl):S160-164. PMID: 23153663 | DOI: 10.1016/j.otsr.2012.09.013
• Yeo MH, Seah SJ, Gatot C, Yew A, Lie D. Selective bundle versus complete anterior-cruciate ligament reconstruction: a systematic review and meta-analysis. J Orthop. 2022;33:124-130. PMID: 35983549 | DOI: 10.1016/j.jor.2022.07.015
• Bosco F, Giustra F, Crivellaro M, et al. Is augmentation the best solution in partial anterior cruciate ligament tears? A literature systematic review and meta-analysis. J Orthop. 2022;36:11-17. PMID: 36578974 | DOI: 10.1016/j.jor.2022.11.018
• Giummarra M, Vocale L, King M. Efficacy of non-surgical management and functional outcomes of partial ACL tears. A systematic review of randomised trials. BMC Musculoskelet Disord. 2022;23(1):332. PMID: 35395764 | DOI: 10.1186/s12891-022-05278-w
• Hughes JD, Burnham JM, Hirsh A, Musahl V, Fu FH, Irrgang JJ, Lynch AD. Comparison of short-term Biodex results after anatomic anterior cruciate ligament reconstruction among 3 autografts. Orthop J Sports Med. 2019;7(5):2325967119847630. PMID: 31211150 | DOI: 10.1177/2325967119847630

Frequently Asked Questions About Partial ACL Tears