S39.012S Strain of muscle, fascia and tendon of lower back, sequela

ICD-10-CM S39.012S: Strain of muscle, fascia and tendon of lower back, sequela

ICD-10-CM code S39.012S designates the sequela, or long-term consequence, of a strain to the muscle, fascia, or tendon of the lower back. It is used after the acute healing phase concludes but residual impairment persists. This code is distinct from initial and subsequent encounter phases, as well as separate ligament sprain injuries. 3 5

Plain-language overview

Mechanical back strain involves an injury to the muscles, ligaments, or tendons of the lower back, often resulting from overuse, sudden movements, or improper body mechanics. Acute low back pain may present as back stiffness, decreased movement, and difficulty standing straight. 1 2

What this code represents

The ICD-10-CM code S39.012S is named "Strain of muscle, fascia and tendon of lower back, sequela" and belongs to the ICD10CM system. The semantic type for this concept is classified as an injury or poisoning event. 3 4

The code S39.012S captures long-term consequences or complications arising from a healed lumbosacral strain. Clinicians switch to this sequela code only when the acute healing phase is complete but residual impairment persists, such as chronic weakness, recurrent pain, or functional limitation. 5

Coding details

The S39.012 code series identifies a discrete traumatic or overuse injury to the muscle, fascia, or tendon of the lower back. This is distinct from ligament injuries of the lumbar spine, which are coded under the S33.5XXA code, and non-specific low back pain codes like M54.5. 5

The S39.012 code set includes distinct encounter characters for different phases of care: S39.012A for the initial encounter, S39.012D for a subsequent encounter, and S39.012S for the sequela. These specific seventh characters differentiate the patient's current healing phase. 5

Documentation considerations

Documentation for encounters supporting S39.012S must include the mechanism of injury, anatomical location, symptom onset timeline, and functional limitations. Clinicians link S39.012S to objective findings, time course, and the plan of care to support decision continuity from triage through discharge. 5 6

What the sources add

Clinical literature from the National Center for Biotechnology Information describes mechanical back strain as a specific subtype of back pain resulting from injury or overuse of the spinal muscles, ligaments, tendons, or surrounding soft tissues. The lumbar region is the area most commonly involved in this pathology. 1

While the clinical literature from NCBI describes the general presentation and management of mechanical back strain, the coding sources from Pabau and Sprypt provide the specific ICD-10-CM mapping and encounter rules for S39.012S. This comparison shows how clinical conditions translate into specific sequela coding concepts. 1 5 6

Sources

1. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-25.
2. Low back pain - acute: MedlinePlus Medical Encyclopedia — medlineplus.gov; accessed 2026-07-25.
3. Browse Code Systems — vsac.nlm.nih.gov; accessed 2026-07-25.
4. EVS Explore — evsexplore.semantics.cancer.gov; accessed 2026-07-25.
5. ICD-10-CM Code S39.012A: Lumbosacral Strain Initial Encounter — pabau.com; accessed 2026-07-25.
6. Strain Of Muscle, Fascia And Tendon Of Lower Back, Sequela | ICD-10-CM S39.012S Clinical Guide — sprypt.com; accessed 2026-07-25.