Connective Tissue, Ligaments and Fascia

Part 1 · General anatomy

One recipe behind tendon, ligament and fascia — and why compartments are dangerous

One recipe, many tissues

Bone, cartilage, tendon, ligament, fascia, dermis, capsule, aponeurosis and even blood are all connective tissue. They share a single formula:

Connective tissue = cells + fibres + ground substance, with the matrix, not the cells, doing the work.

What distinguishes one from another is the proportion of the three ingredients and the orientation of the fibres. Change the ratio of collagen to elastin and you get a ligament instead of a tendon. Change the fibre orientation from parallel to interwoven and you get fascia instead of tendon. Add hydroxyapatite and you get bone. Add water and aggrecan and you get cartilage.

Learn the recipe, and the tissues stop being a list.

Learning outcomes

• Classify connective tissue and name the cells, fibres and ground substance of each type.
• Describe collagen synthesis and name the clinically important collagen types.
• Describe the hierarchical structure of tendon and ligament and explain the crimp pattern.
• Interpret the stress–strain curve of dense connective tissue, including the toe, elastic and plastic regions.
• Explain creep, stress relaxation, hysteresis and thixotropy and their clinical applications.
• Compare tendon and ligament in composition, blood supply, innervation and healing.
• Describe the phases and timeline of ligament and tendon healing and the effect of loading.
• Explain the modern model of tendinopathy and justify a loading-based treatment.
• Describe the organisation of superficial and deep fascia, the osteofascial compartments and the retinacula.
• Recognise acute compartment syndrome and state why it is an emergency.
• Evaluate the claims made about fascia in manual therapy against the evidence.

Classification of connective tissue

The functional rule: parallel fibres resist tension in one direction and are therefore found where load direction is predictable (tendon). Interwoven fibres resist tension in many directions and are found where load direction varies (fascia, capsule, dermis).

The ingredients

Figure 1 · What every connective tissue is made of

7.3.1 Cells

7.3.2 Fibres

Collagen types worth knowing:

Collagen synthesis in outline: transcription → preprocollagen → hydroxylation of proline and lysine (vitamin C-dependent) → glycosylation → triple-helix formation as procollagen → secretion → cleavage of terminal propeptides to tropocollagen → self-assembly into fibrils with quarter-stagger overlap (giving the 67 nm banding) → cross-linking by lysyl oxidase (copper-dependent) → fibrils to fibres.

Two clinical consequences: scurvy (vitamin C deficiency) prevents hydroxylation, producing unstable collagen — poor wound healing, wound breakdown, bleeding gums, subperiosteal haemorrhage; and cross-linking increases with age and with non-enzymatic glycation in diabetes, making tissue stiffer, more brittle and less able to remodel — one reason diabetic patients have stiffer tendons, more frozen shoulders and slower connective tissue healing.

7.3.3 Ground substance

An amorphous, hydrated gel of:

• Glycosaminoglycans (hyaluronan, chondroitin sulphate, dermatan sulphate, keratan sulphate)
• Proteoglycans (decorin, biglycan, fibromodulin — the small leucine-rich proteoglycans that regulate collagen fibrillogenesis and interfibrillar sliding)
• Adhesive glycoproteins (fibronectin, laminin, tenascin)
• Tissue fluid

Its functions are to hydrate, to provide the medium for diffusion of nutrients and metabolites, to lubricate the sliding of collagen fibres past one another (the critical interfibrillar distance), and to resist compression.

The mechanism of immobilisation stiffness

Immobilisation reduces GAG and water content in dense connective tissue. Collagen fibres consequently lie closer together, and new collagen is deposited randomly across the existing fibres, forming abnormal cross-links at the intersections. The fibres can no longer glide past one another. Add adhesion formation and the result is the stiff, restricted joint seen after even a few weeks of casting.

This is why controlled early motion is not simply “good for morale”. It maintains interfibrillar distance and GAG content, and orients new collagen along lines of stress rather than randomly. The tissue’s organisation is a direct consequence of the loading applied during healing.

Tendon and ligament

Figure 2 · Tendon and ligament compared

7.4.1 Hierarchical structure of tendon

Tropocollagen → microfibril → subfibril → fibril → fibre (with tenocytes between) → fascicle (surrounded by endotenon) → tendon (surrounded by epitenon and then paratenon or a synovial sheath)

• Endotenon binds fascicles and carries vessels, lymphatics and nerves; it also permits fascicles to slide relative to one another, which is essential to a multi-tendon unit such as flexor digitorum profundus.
• Epitenon covers the whole tendon.
• Paratenon, a loose areolar sheath, surrounds tendons that run straight (Achilles, patellar). Where a tendon turns a corner or passes through a fibro-osseous tunnel, a true synovial sheath with visceral and parietal layers replaces it, connected by a mesotenon or vincula carrying the blood supply.

7.4.2 The crimp pattern

At rest, collagen fibres in tendon and ligament lie in a regular wavy crimp. Under initial load the crimp straightens before the collagen itself is stretched. This is the structural basis of the toe region of the stress–strain curve, and it is the shock-absorbing buffer that protects the tissue from small loads. Most daily activity operates within the toe region.

7.4.3 Tendon compared with ligament

The watershed zones — where tendons fail

Several tendons have a hypovascular segment where degeneration and rupture concentrate:

• Achilles tendon, 2–6 cm above the calcaneal insertion
• Supraspinatus, the “critical zone” ~1 cm medial to its insertion
• Tibialis posterior, posterior and distal to the medial malleolus
• Long head of biceps, in the intertubercular groove

These are the four tendons that rupture spontaneously in middle age, and their locations are not coincidental.

Mechanical behaviour

Figure 3 · How connective tissue behaves over time

7.5.1 The stress–strain curve

Two important derived points. First, the tissue is permanently lengthened once the yield point is passed — which is precisely what a repeatedly sprained ankle ligament has undergone, and why its mechanoreceptor-mediated protective function is impaired even when it “heals”. Second, ligaments fail at their insertion (enthesis) in the immature and in the immobilised, and in mid-substance in the mature, well-conditioned adult — which is why the adolescent sustains a tibial spine avulsion where the adult sustains an ACL mid-substance rupture.

7.5.2 Viscoelastic behaviour

Because connective tissue contains water and a proteoglycan gel, its response is time-dependent, not purely elastic.

Practical consequence. Low-load, long-duration stretch produces more lasting tissue change than high-load, short-duration stretch, and does so with far less risk of microfailure. This is why serial casting, dynamic splints and 20–30 minute positioning programmes are effective in contracture management, and why brief aggressive stretching is not.

A necessary caveat. The acute range-of-motion gain from a single stretching session is now attributed largely to increased stretch tolerance (a sensory adaptation) rather than to lasting tissue lengthening. Genuine structural lengthening — increased fascicle length, increased sarcomeres in series — is achieved much more reliably by eccentric loading at long muscle lengths and by prolonged positioning, not by conventional stretching.

Healing of ligament and tendon

Phases

The essential clinical statement: at 6 weeks a healing ligament may have as little as 50–60% of its final strength, and full maturation takes a year or longer. Scar tissue never fully regains normal properties, typically plateauing at ~70–80% of original tensile strength with more type III collagen, smaller fibril diameter and inferior mechanical behaviour.

Loading is the organising signal

Immobilised healing produces a weak, disorganised, adhesion-bound scar. Controlled progressive loading during remodelling directly increases collagen alignment, cross-link maturation and ultimate tensile strength — the tissue equivalent of Wolff’s law. This principle, established in animal ligament models and confirmed clinically, is the single strongest justification for early, protected, criteria-progressed rehabilitation rather than prolonged rest.

Intra-articular ligaments heal worst. The ACL is bathed in synovial fluid, which lyses the haematoma and prevents the fibrin clot scaffold from forming. It therefore has essentially no capacity for spontaneous healing — the anatomical reason reconstruction rather than repair is the standard approach.

Tendon healing and adhesion

Tendon heals by both intrinsic (tenocyte-mediated) and extrinsic (surrounding sheath and paratenon) mechanisms. The extrinsic route brings vascularity but also adhesions, which bind the tendon to its sheath and destroy gliding. This is the central problem in flexor tendon repair in the hand, and the reason early controlled mobilisation protocols (Kleinert, Duran, and modern early active motion regimes) exist: they apply enough excursion to prevent adhesion without exceeding repair strength. The window is narrow and the protocols are precise; deviating from them costs the patient hand function.

Tendinopathy: the model that changed practice

The old model — “tendinitis”, an inflammatory condition treated with rest, ice and anti-inflammatories — is wrong, and knowing why changes what you do.

Histopathology of chronic tendinopathy shows: collagen disorganisation and fibre separation, increased type III collagen, increased ground substance and proteoglycan, neovascularisation with accompanying neural ingrowth, tenocyte rounding and proliferation, and an absence of the classic inflammatory cell infiltrate. The correct term is tendinosis or, in the umbrella clinical sense, tendinopathy.

The continuum model (Cook and Purdam) describes three overlapping stages that a tendon can move between in either direction:

What this means for treatment:

• Loading is the treatment. Eccentric protocols (Alfredson), heavy slow resistance and progressive tendon-loading programmes all outperform rest.
• Complete rest is harmful — it reduces tendon capacity and worsens the underlying problem.
• Corticosteroid injection gives short-term relief but is associated with worse medium- and long-term outcomes and higher recurrence in most tendinopathies; it is not a first-line intervention.
• Compressive load matters as much as tensile load. Insertional tendinopathies (Achilles insertional, gluteal, hamstring origin, tibialis posterior) are aggravated by compression of the tendon against bone in end-range positions — so deep stretching into that position is often exactly the wrong thing.
• Pain is a poor guide to tissue state. Load management is guided by the 24-hour response, not by pain during the exercise.

Fascia

Figure 4 · Fascial layers and the compartments of the thigh

7.8.1 Superficial fascia (subcutaneous tissue, hypodermis)

Loose areolar and adipose tissue between the dermis and deep fascia. It contains fat, cutaneous nerves and vessels, superficial veins and lymphatics, and in some regions a membranous layer (Scarpa’s fascia of the abdomen, Colles’ fascia of the perineum, the superficial fascial system of the limbs) and skin ligaments (retinacula cutis) anchoring skin to deep fascia.

Clinical relevance: it is the plane of subcutaneous oedema (hence pitting oedema and the compartment for lymphoedema), the layer mobilised in skin-rolling and soft tissue techniques, and the plane in which superficial veins can be harvested or cannulated. The membranous layer of the perineum (Colles’ fascia) and its attachments determine the direction in which extravasated urine can spread — a classic anatomical point.

7.8.2 Deep fascia

A tough, dense irregular sheet investing muscles, and continuous throughout the body. Its several roles:

7.8.3 Compartments and compartment syndrome

Because deep fascia is strong and essentially inextensible, the compartments it forms are closed spaces. Any increase in their contents raises pressure.

Acute compartment syndrome — a limb-threatening emergency

Mechanism. Bleeding or oedema within a closed compartment raises intracompartmental pressure above capillary perfusion pressure. Perfusion fails, causing ischaemia, which causes further oedema, which raises pressure further — a vicious cycle. Irreversible muscle necrosis begins at approximately 4–6 hours; nerve damage begins earlier.

Crucially: distal pulses are usually PRESENT. Arterial pressure far exceeds the compartment pressure that occludes capillaries. A palpable pulse does not exclude compartment syndrome, and waiting for pulselessness means waiting until the limb is lost.

The cardinal features — the 5 Ps are late and unreliable. The early signs are:

• Pain out of proportion to the injury, escalating, not relieved by analgesia — the earliest and most important sign
• Pain on passive stretch of the muscles in the compartment — the most reliable clinical sign
• Pressure: a tense, tender, swollen compartment
• Paraesthesia in the distribution of the nerve traversing the compartment — the first objective sign
• Paresis, pallor and pulselessness are late and indicate an already-damaged limb

Common causes: tibial fracture (the commonest), forearm fracture (especially supracondylar humeral fracture in children), crush injury, reperfusion after vascular repair, tight casts and dressings, burns, and prolonged limb compression.

What a physiotherapist must do. Do not elevate above heart level (this reduces perfusion pressure further); do not apply ice or compression; split or remove any constricting cast or dressing; do not “work through” the pain; and escalate immediately. Definitive treatment is emergency fasciotomy. The late consequence of a missed compartment syndrome is Volkmann’s ischaemic contracture — fibrotic replacement of the flexor compartment producing a permanently clawed, useless hand.

Chronic exertional compartment syndrome is a different entity: exercise-induced pressure rise causing predictable, reproducible exertional pain and paraesthesia that resolves within minutes of stopping. It is a diagnosis made on exertional pressure measurement, and it responds to gait retraining in some cases and to elective fasciotomy in others.

7.8.4 The thoracolumbar fascia

Worth naming specifically because of its role in trunk mechanics. Classically described in three layers (posterior, middle and anterior) enclosing the erector spinae and quadratus lumborum. Its posterior layer receives latissimus dorsi, the contralateral gluteus maximus, and the aponeuroses of transversus abdominis and internal oblique. It is therefore the connective tissue node through which trunk and limb forces are transmitted diagonally across the body, and the anatomical basis of the posterior oblique sling.

It is also densely innervated, with free nerve endings and nociceptors, and has been demonstrated to be a plausible source of non-specific low back pain in its own right — a more defensible claim than most made about fascia.

7.8.5 Fascia in manual therapy: what the evidence supports

Fascia has attracted a large body of claim, and the honest position is a mixed one:

Supported by evidence:

• Fascia is continuous, richly innervated (with free nerve endings, Ruffini and Pacinian corpuscles, and sympathetic fibres) and is a genuine sensory organ
• It transmits force between muscles and across regions (myofascial force transmission is demonstrable)
• It contains myofibroblasts and can contract slowly, and its stiffness alters with hydration, temperature and loading
• Manual techniques produce reliable short-term changes in perceived stiffness, range and pain

Not supported:

• That manual pressure “releases adhesions”, “breaks down scar tissue” or plastically deforms fascia. The forces required to deform dense fascia meaningfully are far beyond what a therapist’s hands can apply
• That specific fascial “lines” or “trains” can be selectively stretched or that a distant fascial restriction can be palpated with any reliability. Inter-rater reliability of fascial and tissue-texture palpation is consistently poor
• That fascial technique is superior to exercise for any musculoskeletal condition

The defensible synthesis: manual and myofascial techniques are best understood as producing neurophysiological effects — altered mechanosensitivity, descending inhibition, autonomic change, and improved movement tolerance — which create a window in which active loading can be delivered. That is a legitimate and useful role. It is not the same as the mechanical claim usually made for it, and being clear about the difference is part of practising honestly.

Where students consistently go wrong

• Thinking fascia is inert packing. It is innervated, force-transmitting and clinically significant.
• Confusing dense regular with dense irregular. Tendon and ligament are regular; fascia, capsule, dermis and periosteum are irregular.
• Forgetting the toe region. Most normal activity never leaves it.
• Assuming a “healed” ligament at 6 weeks is normal. It may have 50–60% of final strength, and maturation takes a year.
• Calling tendon overuse “tendinitis”. There is no inflammatory infiltrate; it is a degenerative and failed-healing process.
• Resting a tendinopathy. Load is the treatment.
• Stretching an insertional tendinopathy into end range. That compresses the tendon against bone and aggravates it.
• Waiting for pulselessness in suspected compartment syndrome. Pulses are usually present. Pain on passive stretch is the sign.
• Elevating a limb with suspected compartment syndrome above heart level. This reduces perfusion pressure.
• Claiming manual therapy breaks down adhesions. The forces required are not achievable by hand.

Check yourself

15 questions on this chapter. Tap one to see the answer and the reasoning.

Quick review

Further reading

Chapter 7 of 24 · Human Anatomy · Physiotherapist India Next: Chapter 8 — Skin, and How the Body Forms: skin layers and repair, the germ layers, and why one nerve root has both a muscle and a skin patch.

Reviewed by the Physiotherapist India Team. · Human Anatomy contents